Altered expression of the bacteriophage T4 gene 41 (primase-helicase) in an Escherichia coli rho mutant.

Bacteriophage T4 gene 41 protein is an essential replication protein, part of the primase-helicase required for lagging strand DNA synthesis. In a T4+ infection, 41 RNA is first expressed as a polycistronic transcript attached to the upstream RNA of genes uvsX (recombination protein) and 40 (stimulates head formation (Hinton, D. M. (1989) J. Biol. Chem. 264, 14432-14439). As infection proceeds, less of the upstream RNA extends into gene 41 due to an RNA 3' end, approximately equal to 60 bases downstream of uvsX. DNA sequence analysis of this region positions this end within gene 40, immediately after a GC-rich hairpin. This end probably arises from host factor-dependent transcription termination or RNA processing since it is observed in RNA expressed by a uvsX-40-41 plasmid in vivo, but is not seen after in vitro transcription with purified Escherichia coli RNA polymerase. The E. coli transcription termination (rho) mutant rho026 has been characterized as a rho mutation whose terminating activity is not effectively overcome by phage lambda antitermination (Das, A., Gottesman, M. E., Wardwell, J., Trisler, P., and Gottesman, S. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 5530-5534). During a T4+ abortive infection of rho026, the levels of some phage proteins, including 41, are depressed; a T4 phage mutant in goF gives wild type protein patterns in rho026 (Stitt, B. L., and Mosig, G. (1989) J. Bacteriol., in press). The RNA analyses presented here demonstrate that the severalfold decrease in 41 protein in rho026 is accompanied by a similar decrease in 41 RNA. There is both a general reduction in polycistronic uvsX-40-41 RNA and a 2-2.5-fold increase in the proportion of uvsX RNA ending at the 3' end. Infection of rho026 by T4 goF1 returns the relative amount of RNA reading into 41 versus that stopped to near a wild type level. These results suggest that host rho and the T4 goF are involved in the expression of T4 41 RNA.