Nucleotide Sequence of the Simian‐Virus‐40 DNA Region Coding for the Carboxyl‐Terminal Part of the T Antigen

Fragment Hind‐B‐C2, the second largest DNA restriction fragment generated by digestion of fragment Hind‐B with the endo R ·EcoRII enzyme, represents 4.4% of the Simian virus 40 (SV40) genome. The complete nucleotide sequence (231 base pairs) of this fragment has been determined by application of the procedure of Maxam and Gilbert (1977). This region is believed to code for the carboxyl‐terminal part of the T antigen. On the basis of the termination code words in the strand with the same polarity as the early mRNA, two open reading frames for translation could be defined. Only one of these, however, extends through the adjacent Hind‐B‐Ci fragment and is therefore believed to dictate the primary structure of the T antigen. It terminates within Hind‐B with a TAA signal. The region, determined by the second open frame, is large enough to code for a protein of Mr about 11000. The regions in SV40 DNA from which the non‐translated regions of the early and late mRNAs are transcribed overlap over nearly their entire length. Although this spacer region is very (dA + dT)‐rich, a secondary structure model can be proposed which is centered around map position 0.17. The RNA copy of the untranslated region also contains the sequence A‐A‐U‐A‐A‐A, common to all other eukaryotic mRNA molecules sequenced so far; it is present once on the late mRNA and twice on the early messenger RNA. Also a sequence of 6 or 7 successive thymidine residues is present in the early and late DNA strand respectively, 131 and 95 nucleotides beyond the polypeptide termination codons, and these may perhaps play a role in termination of transcription. Of particular interest may be the carboxyl terminus of the T antigen; the terminal tryptic peptide is 10 residues long, six of which are proline.