Nucleotide sequences of the 5′ and 3′ termini of bacteriophage T7 early messenger RNAs synthesized in vivo: Evidence for sequence specificity in RNA processing

Abstract

Sequence analysis of the 5′ and 3′ termini of bacteriophage T7 early RNAs synthesized in vivo supports a model for transcription of the early region in which a large precursor molecule is processed to yield monocistronic messengers plus several overlapping “initiator” RNAs (Dunn & Studier, 1973a). The 5′ terminal oligonucleotides, isolated by a two-dimensional electrophoretic technique, are pGpApUp for the messenger RNAs of genes 0.3, 0.7., and 1. The two largest initiator RNAs begin pppApUpCpGp and pppGp, respectively. 3′ terminal oligonucleotides, isolated on columns of dihydroxyboryl-substituted cellulose, are CpCp(Cp)UpUpUpApUOH for all of the RNA species except the last messenger in the early region. 3′ terminal sequence heterogeneity, arising from the addition of several adenylic acid residues to the hydroxyl end of the above sequence, is often observed. The identity of the 5′ and of the 3′ termini of the cleaved messenger species implies that the processing of T7 early RNAs is a sequence specific event.