REGULATION OF INTEGRATION BY COLIPHAGE-LAMBDA - ACTIVATION OF INT TRANSCRIPTION BY THE CLL AND CLLL PROTEINS

Transcription of the int-xis region of Coliphage λ was studied both in the intact phage and in the EcoRI λ C fragment carried by a ColE1 plasmid. This study shows that two species of RNA are transcribed from the int-xis region: a short one, about 3 S, transcribed constitutively and designated lin (leader of int) RNA, and a long one, about 15 S, which is designated int RNA. Synthesis of the 15 S RNA requires the products of genes cII and cIII. Both species of RNA are initiated at about 60.4 %λ on the physical phage λ map, indicating that the p1 promoter must be located just outside the right boundary of gene xis. The cII and cIII proteins are not required for the transcription of gene int in the λ int-c mutants. Based on the present data and the previous findings on the role of the cII and cIII proteins in the regulation of cI transcription, we propose the cII/cIII-mediated antitermination of the RNA leader sequences as the main regulatory mechanism for the establishment of lysogeny by bacteriophage λ. However, the observed stimulation of lin RNA synthesis, most probably mediated by the cII and cIII products, may also play an important regulatory role. © 1979.