Small Ribonucleic Acids of Escherichia coli

Abstract Escherichia coli RNA molecules in the size range of 70 to 400 nucleotides have been characterized by polyacrylamide gel electrophoresis and by RNase T1 (EC 2.7.7.26) finger-printing. RNA labeled by 32PO43- for 20 min is separated into about 20 bands by electrophoresis in 5, 10, and 20% polyacrylamide gels; many of them represent pure RNA species. Some correspond to known molecules such as tRNAs, 5 S RNA, 4.5 S RNA, and 6 S RNA, but others have not been described previously. The amounts of these latter molecules are low, usually less than 10% of the level of 5 S RNA. One molecule, with electrophoretic mobility similar to 5 S RNA, has a 5'-terminal guanosine triphosphate. Another, with a mobility similar to that of 6 S RNA, contains dihydrouracil. Several different RNA preparation methods give essentially the same results. Two-dimensional polyacrylamide gel electrophoresis (10% → 20% polyacrylamide) was used to purify RNA in the 4 S to 5 S region. This technique is capable of resolving at least 30 different RNA species; many of them are pure tRNA molecules. It allows for direct comparison of the quantities of purified tRNAs and the other molecules described in this paper. Such analysis shows that during 20 min labeling the newly characterized molecules accumulate at levels comparable to many individual tRNAs.