The cloned bacteriophage T4 pin gene functions to stabilize several different kinds of proteins in Escherichia coli bacteria. Incomplete proteins such as puromycyl polypeptides, abnormal but complete proteins such as the A phage tsO protein, and labile eukaryotic proteins encoded by genes cloned in E. coli such as mature human fibroblast interferon are stabilized in cells in which the T4 pin gene is expressed. The cloned T4 pin gene does not seem to affect the turnover of normal E. coli proteins.The introduction of cloned genes into Escherichia coli bacteria for the purpose of producing large amounts of specific proteins not normally present in E. coli cells has led to an examination of various problems associated with the expression of such cloned genes. Difficulties in obtaining expected levels of expression from genes cloned in bacterial cells may be encountered at the levels of stability of the gene and its vector within the host cell (1, 2), transcription of the cloned gene (3-7), and translation of its mRNA into protein (5,6,8 Difco agar, maltose/L bottom agar is identical to maltose/L top agar. Bacteria that were to be assayed for interferon activity were grown in the presence of the appropriate antibiotic(s) in either M9, which contains, per liter: NH4Cl, 1.0 g; KH2PO4, 3.0 g; Na2HPO4, 6.0 g; NaCl, 5.0 g; MgSO4 7H2O, 0.25 g; CaCl2, 0.015 g; glucose, 2.0 g; supplemented with vitamin BI and Casamino acids to final concentrations of 0.001% and 0.5%, respectively, 2059The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

T4 bacteriophage mutants called bypass31 (byp3l) that specifically suppress gene 31 amber mutations have been isolated and characterized. The mechanism by which the byp31 mutation, byp31-1, suppresses gene 31 nonsense mutations does not involve synthesis of gp3l or of a particular gp3l fragment; furthermore, the byp31 allele suppresses all nonsense mutations in gene 31 that have been tested. We detect no unusual properties among the T4 particles made in su-cells by the T4amN54byp31-1 double mutant. These virions, made in the absence of gp31, show normal heat sensitivity, normal sensitivity to osmotic shock, and normal morphology. Specific different gene 31 missense mutants are able to form plaques with high efficiencies on the following two types of host defective cells: (i) Escherichia coli groEL (Tilly et al., Proc. NatI. Acad. Sci. U.S.A. 78:1629-1633, 1981) mutants that block T4 capsid assembly and (ii) E. coli rho mutants in which T4+ heads are assembled, but in which tail production and DNA synthesis are blocked. (Note that not all rho mutants block T4 production [G.

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