Expression and regulation of genes coding for three bacteriophage T4 tail tube-associated proteins.

The assembly and length regulation of the tail tube of bacteriophage T4 requires the function of three proteins: gp29, 48, and 54. Six copies of each protein are found in the completed tail, and the genes for these proteins are adjacent on the T4 genome. Evidence is presented here that gp54 is also a tail tube-associated protein that remains bound to the tail tube after the baseplate is removed by guanidine hydrochloride, suggesting that all three proteins interact structurally. There is a strong polar effect of translation termination mutants in gene 48 upon the expression of the adjacent gene 54, in cis-trans tests. Gene dosage experiments that assay the in vivo expression of these genes show that only gene 48 is expressed at slightly higher than stoichiometric levels during T4 infection. Genes 48 and 54 were placed under the control of a T7 promoter and the corresponding proteins identified. When a frameshift mutation was introduced into gene 48, neither gp48 nor gp54 was made. Transcriptional termination was not the explanation of this result because genes distal to 48 and 54 in the plasmid were expressed. These data suggest that expression of genes 48 and 54 is translationally coupled.