CHARACTERIZATION OF THE MAJOR ALTERED LEADER SEQUENCE OF LATE MESSENGER-RNA INDUCED BY SV40 DELETION MUTANT D1-1811

dl-1811 is a viable SV40 mutant with a 40 base pair deletion that includes the major wild-type capping site of late mRNA at map position 0.72. The late viral mRNAs induced by dl-1811 have now been further characterized by inversed Sl-mapping analysis. The Sl-resistant, 32p-labeled RNA fragments derived from the leader region were examined by fingerprinting and by analysis of RNase T2-generated 5'-terminal cap structures. The results show that most if not all of the mutant leader fragments analyzed have their 5' terminus to the left of the dl-1811 deletion site, i.e., closer to the origin of DNA replication. The major altered leader fragment is a continuous transcript from the DNA in the region 0.716 to 0.761 map unit and its 5′ terminus has been precisely mapped at nucleotide L29O. The observation that the cap structure of the major altered leader is only a minor cap species in wild-type late RNA suggests regulation in the use of different capping sites in SV40. © 1979 Information Retrieval Limited.