Uracil uptake by Saccharomyces cerevisiae is mediated by the FUR4-encoded uracil permease. The modification of uracil permease by phosphorylation at the plasma membrane is a key mechanism for regulating endocytosis of this protein. This modification in turn facilitates its ubiquitination and internalization. Following endocytosis, the permease is targeted to the lysosome/vacuole for proteolysis. We have previously shown that uracil permease is phosphorylated at several serine residues within a well characterized N-terminal PEST sequence. In this report, we provide evidence that lysine residues 38 and 41, adjacent to the PEST sequence, are the target sites for ubiquitination of the permease. Conservative substitutions at both Lys38 and Lys41 give variant permeases that are phosphorylated but fail to internalize. The PEST sequence contains potential phosphorylation sites conforming to the consensus sequences for casein kinase 1. Casein kinase 1 (CK1) protein kinases, encoded by the redundant YCKI and YCK2 genes, are located at the plasma membrane. Either alone supports growth, but loss of function of both is lethal. Here, we show that in CK1-deficient cells, the permease is poorly phosphorylated and poorly ubiquitinated. Moreover, CK1 overproduction rescued the defective endocytosis of a mutant permease in which the serine phosphoacceptors were replaced by threonine (a less effective phosphoacceptor), which suggests that Yck activity may play a direct role in phosphorylating the permease. Permease internalization was not greatly affected in CK1-deficient cells, despite the low level of ubiquitination of the protein. This may be due to CK1 having a second counteracting role in endocytosis as shown by the higher turnover of variant permeases with unphosphorylatable versions of the PEST sequence. Uracil uptake by Saccharomyces cerevisiae is mediated by the FUR4-encoded uracil permease. The modification of uracil permease by phosphorylation at the plasma membrane is a key mechanism for regulating endocytosis of this protein. This modification in turn facilitates its ubiquitination and internalization. Following endocytosis, the permease is targeted to the lysosome/vacuole for proteolysis. We have previously shown that uracil permease is phosphorylated at several serine residues within a well characterized N-terminal PEST sequence. In this report, we provide evidence that lysine residues 38 and 41, adjacent to the PEST sequence, are the target sites for ubiquitination of the permease. Conservative substitutions at both Lys38 and Lys41 give variant permeases that are phosphorylated but fail to internalize. The PEST sequence contains potential phosphorylation sites conforming to the consensus sequences for casein kinase 1. Casein kinase 1 (CK1) protein kinases, encoded by the redundant YCKI and YCK2 genes, are located at the plasma membrane. Either alone supports growth, but loss of function of both is lethal. Here, we show that in CK1-deficient cells, the permease is poorly phosphorylated and poorly ubiquitinated. Moreover, CK1 overproduction rescued the defective endocytosis of a mutant permease in which the serine phosphoacceptors were replaced by threonine (a less effective phosphoacceptor), which suggests that Yck activity may play a direct role in phosphorylating the permease. Permease internalization was not greatly affected in CK1-deficient cells, despite the low level of ubiquitination of the protein. This may be due to CK1 having a second counteracting role in endocytosis as shown by the higher turnover of variant permeases with unphosphorylatable versions of the PEST sequence. casein kinase 1 Phosphorylation of proteins at Ser, Thr, and Tyr residues is one of the most frequent forms of posttranslational modification in eukaryotic cells, and it is linked to the control of a multitude of cellular functions. The completion of the Saccharomyces cerevisiae genome sequencing project made it possible to determine that there are 113 conventional protein kinase genes, corresponding to 2% of the total number of genes. Casein kinase 1 (CK1)1 protein kinases are ubiquitous and abundant Ser/Thr-specific protein kinases. The activity of this protein kinase family relies upon upstream acidic and/or phosphorylated amino acids for substrate recognition (1Tuazon P.T. Traugh J.A. Adv. Second Messenger Phosphoprotein Res. 1991; 23: 123-164PubMed Google Scholar). The members of each subfamily differ in substrate selectivity and subcellular location. There are four CK1 proteins in S. cerevisiae, forming two essential gene pairs (2Hoekstra M.F. Liskay R.M. Ou A.C. DeMaggio A.J. Burbee D.G. Heffron F. Science. 1991; 253: 1031-1034Crossref PubMed Scopus (154) Google Scholar, 3Wang P.C. Vancura A. Mitcheson T.G. Kuret J. Mol. Biol. Cell. 1992; 3: 275-286Crossref PubMed Scopus (79) Google Scholar, 4Robinson L.C. 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The similar and functionally interchangeable kinases encoded by these two genes are peripheral plasma membrane proteins and are most probably anchored to the plasma membrane by a carboxyl-terminal isoprenyl modification (6Vancura A. Sessler A. Leichus B. Kuret J. J. Biol. Chem. 1994; 269: 19271-19278Abstract Full Text PDF PubMed Google Scholar). The location of the Yck2p isoform at the membrane is dynamic, with this protein showing cell cycle-specific localization to sites of polarized growth (7Robinson L.C. Bradley C. Bryan J.D. Jerome A. Kweon Y. Panek H.R. Mol. Biol. Cell. 1999; 10: 1077-1092Crossref PubMed Scopus (61) Google Scholar). Wild-type levels of Yck activity are required for efficient constitutive endocytosis of the pheromone receptor Ste3p (8Panek H.R. Stepp J.D. Engle H.M. Marks K.M. Tan P.K. Lemmon S.K. Robinson L.C. EMBO J. 1997; 16: 4194-4204Crossref PubMed Scopus (129) Google Scholar). 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D. Mol. Cell. Biol. 1998; PubMed Scopus Google a that is required for subsequent internalization B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). the permease is targeted to the for C. D. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). Permease ubiquitination is mediated by the essential which is also required for the ubiquitination of other yeast the and C. C. B. Mol. PubMed Scopus Google Scholar, 1997; PubMed Google Scholar, H. C. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, A. J. Cell Biol. 1999; PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). with two target of by EMBO J. 1997; 16: PubMed Scopus Google Scholar). of the of ubiquitination of the and Ste3p J. S. L. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and several and A. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, EMBO J. 1997; 16: PubMed Scopus Google Scholar, B. J. Cell Sci. 1999; PubMed Google a similar with in each a number of target of We have shown that internalization is upon the permease phosphorylated at several serine residues within a of amino acids as the PEST sequence C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). We in this the role of 38 and 41, N-terminal to the PEST sequence, in internalization of the permease. The ubiquitination of and is by phosphorylation (9Hicke L. Zanolari B. Riezman H. J. Cell Biol. 1998; 141: 349-358Crossref PubMed Scopus (246) Google Scholar, C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). The kinases that have to be In this we that CK1 activity the phosphorylation of the which is for its subsequent ubiquitination and internalization. The a was J. M. J. PubMed Scopus Google the and and have been L.C. S. Culbertson M.R. Mol. Cell. Biol. PubMed Scopus Google Scholar). The uracil permease is in and that the permease were for of permease activity and for the of the protein C. C. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar). The C. D. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google the gene the control of the The and its the YCK2 gene the control of the were by were as by D. A. R.A. Res. 1992; PubMed Scopus Google Scholar). Cells were at for in yeast amino acids and with The was 2% One to of the as by the and by the for the other R.M. PubMed Scopus Google Scholar). were by for site by the and by each two mutant were to and two yeast were for each mutant Uracil uptake was in growing as previously C. C. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar). was with for at and which were with and for Cell were and proteins were by as previously C. D. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google the residues of and M. of and were with a by in the growth were by in the of and to plasma as previously B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). proteins were by as previously C. D. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). it has been shown that uracil permease is phosphorylated its at the cell C. C. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar). The permease is phosphorylated at a sequence to at the of 1 This sequence has been shown to be essential for uracil permease turnover C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). The sequence contains potential phosphorylation sites conforming to consensus sequences for kinases CK1 the are phosphorylated and and 1 other potential sites for casein kinase 1 phosphorylation are in the of the permease. One is located in the of the protein and the other is in the of the permease the C. Mol. 1996; PubMed Scopus Google Scholar). has been to the role of several in both of the to the potential casein kinase 1 phosphorylation sites C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). of the corresponding with it was shown that only located in a PEST to in the permease were phosphoacceptors for turnover of the protein. We a mutant the YCK1 gene and a of the YCK2 to to the role of Yck activity in the phosphorylation of the permease. we the cell of uracil permease in and Permease was control of the by to the of at and for to Uracil uptake was for The level and of permease activity were similar in and mutant not CK1 not the of uracil permease to the plasma membrane. We the phosphorylation of in and at 1 Phosphorylation of the permease in that and which upon C. C. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). We the of the and mutant The loss of and Yck2p the of with the loss of and the of in phosphorylation was also to a of the kinase isoforms were the was in at not serine residues of the PEST to variant in a level of phosphorylation of the permease in C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google and The of the variant was affected that of in cells, and it was not affected by in show that Yck activity a direct role in phosphorylating the sequence and that and Yck2p to the phosphorylation of the protein. kinases may also the permease the level of phosphorylation of in was in and of the permease is a cell required for internalization B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). of the permease is upon the protein phosphorylated in its PEST C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). We whether a of Yck kinase activity the level of permease The membrane of at were as a of four of the permease 1 It has previously been that these to and B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, EMBO J. 1997; 16: PubMed Scopus Google Scholar). The of permease was to the of but the were to as a to were and at and to for Wild-type a higher of to the permease at were in variant at not C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). to the not but in that the of to the permease is not by the phosphorylation of the PEST sequence. at and variant permeases with similar in each and were There were similar levels in in and as for this unphosphorylatable that was in but less in This suggests that the phosphorylation of serine residues by Yck activity within the PEST is required for the ubiquitination of the permease. determine whether in the YCK2 genes affected we permease activity the of protein in and at and to for The of a in uracil uptake in at The in uracil uptake was less in to the The loss of permease activity that the in Yck activity the at the plasma membrane. at the of were by degradation was in internalization and the subsequent degradation of the permease directly Yck kinase The defective phosphorylation and ubiquitination of in is of the of for a variant permease with for serine substitutions in the PEST sequence C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). of this variant was internalization was affected in despite and and This suggests that Yck proteins may also be required for the of of the endocytosis This was by the in of variant permeases to phosphorylation within the PEST sequence We the of the in which of the in the PEST sequence are replaced by the C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). the of ubiquitination not and internalization of the variant was to that of in to this protein was in to the We the turnover of the variant permease. to the of phosphoacceptors in the PEST sequence, the variant is poorly 1 protein was in uracil uptake was the in the of to cells, a in uracil uptake was that the of the variant be within the of the the of phosphorylation the of permease activity This that Yck activity may a in the internalization and suggests that the of at the plasma membrane in may be due to the counteracting of this possible second of by We whether of the serine residues within the PEST sequence are the phosphoacceptors for casein kinase a variant in which the in the PEST sequence been replaced by kinases also but less and we have previously that the variant protein is poorly phosphorylated C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). we the phosphorylation of and variant proteins in with and of the YCK2 gene one of the two casein kinase 1 proteins The overproduction of Yck2p the of with the loss of and the of corresponding to higher levels of phosphorylation of the protein. overproduction of the protein also a in but to a with the of threonine residues to be We the level of internalization of and variant proteins in and The of a in the uracil uptake of permease Permease with the in uracil uptake Uracil uptake less in the The was The also the permease overproduction of in the of internalization and degradation of was despite the protein that a level of phosphorylation of is for internalization. In a in uracil uptake was in the to the internalization Yck2p was the variant protein was less to The in the of the in the of permease the of turnover of the variant was in Yck2p and was similar to that of that may be able to the PEST of directly in We previously that the of the PEST ubiquitination of a variant of the PEST sequence with substitutions but less the permease C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google The PEST sequence is by two lysine residues and 1 one of which was the PEST sequence was This may directly the of ubiquitination the of to with of the of EMBO J. 1997; 16: PubMed Scopus Google Scholar). and permease were in of genes and a mutant a as of This suggests that two lysine residues in permease as but these lysine residues are not Lys41 to the PEST is in similar to the of the we and which is to the We to these with but we that two were required for ubiquitination in we in The corresponding variant proteins were for of ubiquitination and we the cell of the variant permeases the by to the of Uracil uptake was for Permease activity with the the permease not the not the of uracil permease to the plasma membrane. We the ubiquitination of the of membrane a of four with the permease and corresponding to and The was in the that the lysine to PEST is not a target for In the of a second in a with two corresponding to and The was with of Lys38 substitutions of in the loss of similar with was with substitutions at Lys38 and that Lys38 and Lys41 are the two target sites for ubiquitination of the permease. also that of the permease the of each two in to each of the two target We the of the permease of protein The of a in permease activity Permease in to the in uracil uptake In the in uracil uptake was less in able to to two Lys38 The loss of permease activity that the to one of the two the at the plasma membrane. The corresponding also permease the two target were loss in uracil uptake was and the of permease the of the were the PEST was C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). are with the of of in the mutant permease. show that Yck activity is in the phosphorylation of the PEST of the in facilitates the ubiquitination and subsequent endocytosis of the permease. We also that the of casein kinase phosphorylation and ubiquitination are has only a internalization of the permease. In this report, we also provide evidence that phosphorylation of at PEST to of at Lys38 and proteins are in of casein kinase 1. a phosphorylation sites and sites phosphorylated in has been shown for proteins. The plasma membrane was the substrate of casein kinase 1 to be in and a loss of Yck function the of activity by J. J. A. M. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar). It has been shown that phosphorylation of the at serine residues at is in a consensus site for casein kinase 1) is by in the YCK1 and YCK2 genes A. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The Yck proteins are also required for phosphorylation of the α-factor receptor, Ste2p, and phosphorylation of this receptor α-factor receptor internalization (9Hicke L. Zanolari B. Riezman H. J. Cell Biol. 1998; 141: 349-358Crossref PubMed Scopus (246) Google Scholar). It is unknown whether casein kinase 1 directly phosphorylates The PEST sequence of contains potential phosphorylation sites conforming to consensus sequences for kinases casein kinase 1. other potential CK1 sites are in the in the and of the protein. of the corresponding by that only located in a PEST were phosphoacceptors for turnover of the protein C. D. Mol. Cell. Biol. 1998; PubMed Scopus Google Scholar). we show that modification and internalization of the permease phosphorylation, that and Yck2p play a direct role in phosphorylating the permease. the defective turnover of a variant in which in the PEST were replaced with threonine (a less effective This for the direct of Yck proteins in the phosphorylation of the PEST of the permease in the of phosphorylation mechanism be consensus sites for phosphorylation have that provide recognition for CK1 activity H. Graves P.R. Roach P.J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). substrate in may the activity of CK1 to of other protein kinases in a in which a phosphorylation a recognition site for The permease PEST sequence has two of We have previously shown that in of the two of with the the of the permease and that the of substitutions in the two are potential target sites for CK1 may be in of the two of PEST the of serine as a recognition this is the Yck proteins may well be in substrate phosphorylation the PEST in a that permease variant permease with of the in the PEST sequence replaced by was to be poorly and at the cell we show that the permease was also poorly in its at the plasma membrane shown by the permease activity of protein was and not with its Moreover, the loss of of unphosphorylatable PEST of the permease upon in evidence for control by Yck proteins of the internalization of the permease. The of at the plasma membrane a that contains mutant with in and have been shown to defective internalization of at C. D. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar, B. C. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, B. Mol. Biol. Cell. 1997; PubMed Scopus Google Scholar). of phosphorylation may for the of Yck two protein kinases, M. J. Cell Biol. 1999; PubMed Scopus Google and S. C. D.G. J. Cell Biol. 1999; PubMed Scopus Google were shown to be with and to the in It is possible that CK1 the of by regulating the that CK1 and kinases Panek (8Panek H.R. Stepp J.D. Engle H.M. Marks K.M. Tan P.K. Lemmon S.K. Robinson L.C. EMBO J. 1997; 16: 4194-4204Crossref PubMed Scopus (129) Google that function is required in and that Yck activity may be required for a that is to a a role in at the plasma membrane in the are only affected in the endocytosis of Ste2p, and the P.K. J. Cell Biol. PubMed Scopus Google Scholar, J. 1999; PubMed Google and internalization has been shown to be in the mutant cells, that endocytosis Riezman H. J. Cell Sci. 1998; PubMed Google Scholar). it that Yck proteins are in the internalization of a control The role of in the of cell proteins uracil permease has to the that as a for endocytosis M. 1996; PubMed Scopus Google Scholar). It was that the of is in the endocytosis of L. EMBO J. PubMed Scopus Google Scholar). that a receptor that may be in the internalization The of a receptor for proteins may be to the number of This that the of two adjacent at 38 and by both the ubiquitination and internalization of This suggests that these two residues are the for one of the two lysine residues the and are not are with that is with of EMBO J. 1997; 16: PubMed Scopus Google and that these are with two Moreover, the less efficient internalization of the corresponding variant permeases suggests that and of the permease is not for internalization. The of internalization in with one of the two target replaced with was similar to that in with as the of EMBO J. 1997; 16: PubMed Scopus Google Scholar). the of internalization of the permease is similar whether it is with two as a of two as two at two This is with the by L. that of the receptor, Ste2p, is to its internalization J. S. L. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). is the sequence for the internalization of yeast cell proteins. sequence was to be and for endocytosis of a J. H. Zanolari B. Riezman H. Mol. Biol. Cell. PubMed Scopus Google Scholar). this sequence, the was to be for ubiquitination and to be one of the ubiquitination sites in the receptor J. S. L. Mol. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). similar to the sequence, was in S. EMBO J. 1997; 16: PubMed Scopus Google Scholar). This is within a acidic required for ubiquitination of the protein. The to be of the a within it only a turnover the of lysine lysine residues in similar and were shown to be with other in the ubiquitination and turnover of the A. J. Cell Biol. 1999; PubMed Scopus Google Scholar). In this report, we show that one of the two lysine residues required for ubiquitination is also in a similar sequence, We that the lysine residues in a are probably for the ubiquitination of plasma membrane proteins. target are located the PEST in and is of the of Phosphorylation within a sequence in a of the Ste3p receptor has been shown to be for ubiquitination of lysine residues within that sequence that function J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). This is of the for the for which ubiquitination two adjacent located only residues the two forming of a recognition for the Y. H. A. S. S. F. A. Y. EMBO J. 1997; 16: PubMed Scopus Google Scholar). It is possible that the is by the phosphorylated PEST of in ubiquitination at as binding M. C. A. PubMed Scopus Google and a binding J. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). a growing number of yeast plasma membrane proteins have been shown to be by the have not been shown to directly with this these proteins not which are by the Ste2p, and may phosphorylated with one of the of with a that a M. Science. 1999; PubMed Scopus Google Scholar). It is also possible that these plasma membrane proteins with proteins. We are these two with the PEST sequence of uracil permease. We are to C. for and of the We are to J. M. for and for with the We J. for We for
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