RNA synthesis during bacteriophage SPO1 development: II. Some modulations and prerequisites of the transcription program

Abstract

A detailed RNA-DNA hybridization-competition analysis of the program of transcription during bacteriophage SPO1 development has been made. The synthesis of six classes of viral RNA ( e, em, m, m 1 l, m 2 l, and l) has been distinguished previously ( Gage and Geiduschek, 1971). In this paper some of the modulations and pre-requisites of transcription of these classes of viral RNA are analyzed. It is shown that within the class of em transcripts, not all polynucleotide sequences first appear at the same time. A comparable asynchrony of first appearance occurs with e RNA. Between the time of repression of e transcription and the onset of viral DNA replication, em RNA becomes 2.5 times more abundant; this is concomitant with increased viral transcription. In late development, m 1 l, m 2 l, and l RNA are transcribed at constant relative rates, yet m 1 l RNA becomes less abundant during this period, probably because of decreased stability. The role of protein and viral DNA synthesis in the transcription program have also been analyzed. Formation of the viral DNA-host RNA polymerase complex ensures synthesis of e and em RNA, but all subsequent turn-on and shut-off events require some postinfection protein synthesis. In cells infected with a DNA negative mutant, the transcriptional program appears normal except that l RNA is not made. The time of first initiation of RNA chains, whose translation products are essential for two viral functions, has been measured with the use of rifamycin. The two functions in question are the shut-off of host DNA synthesis and the replication of viral DNA. The first initiation of their conjugate sets of messages coincides with the first appearance of m and m 1 l RNA. We conclude that transcription of one or both of these classes of RNA is controlled positively, at RNA chain initiation.