Early intermediates in bacteriophage lambda prohead assembly.

The morphogenesis of phage λ proheads is under control of the four phage genes B, C, E, and Nu3 and the host cell gene groE. To determine if the assembly of the prohead proceeds via the formation of subassembly complexes, the proteins synthesized in E. coli following infection with λ phage were analyzed by analytical sedimentation in glycerol gradients. The phage-induced proteins were labeled in vivo by incorporation of ³⁵S-labeled Met, and the protein composition of the fractions of the gradients was determined by electrophoresis in polyacrylamide gels followed by autoradiography. It was found that gpB sediments at positions corresponding to 25 S and 30 S, and that two polypeptides, derived from gpC, sediment as 30 S. The 25 S and 30 S complexes accumulate in λE^?-infected cells, but no complexes are formed in λE^?B^?-infected cells. The formation of the 30 S complex, but not of the 25 S complex, is blocked in λE^?C^?-infected cells. A host-controlled band cosediments with gpB in the 25 S position, but not in the 30 S position. Using a recombinant λ phage carrying the host groE gene, the band cosedimenting with gpB was identified as the product of the groE gene. The groE gene product and gpB seem to form a complex since amber peptides of gpB (about $\text{2}\text{5}$ the size of the wild-type product) still cosediment with gpgroE in the 25 S position of the gradient. The formation of the 30 S complex is blocked, and the synthesis of the 25 S complex strongly inhibited, in groE missense mutant cells infected with λE^? The results suggest that gpB and gpgroE interact at an early stage in prohead morphogenesis to form a 25 S complex which seems to be a precursor of a 30 S gpB- and gpC-containing complex. The existence of a gpB-gpC complex suggests that these two gene products interact directly. Since gpB is located in the head-tail junction of the phage, it seems highly likely that the polypeptides pX1 and pX2, derived from gpC, are also located at the head-tail junction.