Pre-early proteins of bacteriophage T5: Structure and function

The molecular weights of three previously detected pre-early T5 proteins (1a, 1b, and 1c) and their subunits have been determined from their effective electrophoretic mobilities in polyacrylamide gels. Protein 1b displays a molecular weight of 18,200 daltons but can be dissociated into subunits of 11,400 daltons. Hence, protein 1b is probably a dimer with identical subunits. Protein 1c, on the other hand, is monomeric since it displays molecular weights of 18,500 and 19,000 daltons before and after denaturation, respectively. Protein 1a was resolved into two oligomeric proteins, 1a(A1) and 1a(A1:A2) with probable molecular weights of 244,000 and 364,000 daltons, respectively. Protein 1a(A1) is composed of identical subunits each with a molecular weight of 57,000 daltons. Protein 1a(A1:A2) is formed from non-identical subunits whose molecular weights are 57,000 and 15,000 daltons. The 57,000 dalton subunit is an essential component of both the 1a(A1) and 1a(A1:A2) oligomeric proteins. T5 amber mutants defective in gene A1 do not induce the synthesis of the 57,000 dalton subunit and, hence, of either the 1a(A1) or the 1a(A1:A2) oligomeric proteins. T5 amber mutants defective in gene A2 do not induce the synthesis of the 15,000 dalton subunit, but do induce the synthesis of the 57,000 dalton subunit. Hence, we conclude that gene A2 mutants do not induce the synthesis of the 1a(A1:A2) protein but do synthesize the 1a(A1) protein. The pleiotropic effect of a mutation in gene Al may be explained in terms of these multiple protein forms.