Transcription during bacteriophage T4 development: Requirements for late messenger synthesis

Abstract

The prerequisites of late T4 messenger synthesis have been investigated in phageinfected Escherichia coli B, using the methods of DNA-RNA hybridizationcompetition. The absolute requirement of some DNA synthesis for viral late messenger synthesis has been demonstrated in three ways: (1) several DNA synthesis-negative (DO) amber mutants located in 3 different segments of the viral chromosome have been shown to be defective in late messenger synthesis in the non-permissive host; (2) when phage DNA synthesis is made thymine dependent by the proper choice of viral mutant and host, viral late messenger synthesis also becomes thymine-dependent, but early messenger synthesis does not; (3) ultraviolet-irradiated T4+ which do not replicate their DNA do not synthesize viral late messenger. However, DNA synthesis and late messenger synthesis are not linearly related. For example, late messenger synthesis can be sustained in cells infected with T4 gene 30 amber mutants in which DNA synthesis has almost ceased. DNA replication is not a sufficient requirement for late messenger synthesis: the function of at least one, and possibly more, "maturation gene" products is also required. Thus, a maturation-defective mutant, lacking the function of gene 55 (am BL 292), synthesizes DNA but no late messenger. A mutant in T4 gene 33 (am N134) is of the same type but "leakier" and eventually makes readily detectable proportions of late viral RNA. A viral dCTPase, the product of T4 gene 56, is synthesized early in normal T4 development. This enzyme helps to prevent the synthesis of cytosine-containing viral DNA. dCTPase-negative T4 amber mutants, even two multiple mutants that synthesize appreciable quantities of viral DNA, are defective in late messenger synthesis. Evidently, two mechanisms must be involved in the synthesis of T4 late messenger: (1) a competent form of DNA must be made available in the infected cell; and (2) one or more "maturation" gene products must act on this competent DNA. T4 gene 55 is likely to specify one such product. © 1968.