Effect of elevated temperature on extended enzyme synthesis induced by bacteriophage T4 amber mutants unable to synthesize deoxyribonucleic acid.

The extended synthesis of early enzymes by the deoxyribonucleic acid-negative amber mutants of bacteriophage T4 after infection of the nonpermissive host Escherichia coli B was prevented by incubating the infected cells at 44 C. This effect did not occur if the incubation temperature was 43 C or less or if the cells were grown and infected in broth rather than minimal medium (C medium). Once early enzyme synthesis had ceased at 44 C, lowering the incubation temperature to 37 C did not occasion resumption of synthesis. Experiments with chloramphenicol at 44 C indicated that increased degradation of early enzymes is an unlikely explanation for the effect. Examination of pulse-labeled ribonucleic acid and polysomes made at 37 and 44 C in infected cells revealed some differences, but at present there is no obvious way in which these differences may be related to the effect on enzyme formation. There was no discernible difference between the ribosomal ribonucleic acid and ribosomes at the two temperatures, nor was there a difference in the cell-free amino acid-incorporating systems isolated from cells infected at the two temperatures as judged by polyuridylic stimulation of phenylalanine incorporation. Incubation of cells infected with T4amN82 at 44 C with protein synthesis blocked by 5-methyltryptophan for 15 min did not prevent the typical pattern of enzyme synthesis at 44 C when the block was reversed by excess l-tryptophan. The relation of this and other observations relative to the effect at 44 C on the synthesis of early enzymes is discussed.