CHARACTERIZATION OF THE HELPER PROTEINS FOR THE ASSEMBLY OF TAIL FIBERS OF COLIPHAGE-T4 AND COLIPHAGE-LAMBDA

Assembly of tail fibers of coliphage T4 requires the action of helper proteins. In the absence of one of these, protein 38 (p38), p37, const ituting the distal part of the long tail fiber, fails to oligomerize. In the absence of the other, p57, p34 (another component of the long t ail fiber), p37, and p12 (the subunit of the short tail fiber) remain unassembled. p38 can be replaced by the Tfa (tail fiber assembly) prot ein (pTfa) of phage lambda, which has the advantage of remaining solub le even when produced in massive amounts. The mechanisms of action of the helpers are unknown. As a first step towards elucidation of these mechanisms, p57 and pTfa have been purified to homogeneity and have be en crystallized. The identity of gene 57 (g57), not known with certain ty previously, has been established. The 79-residue protein p57 repres ents a very exotic polypeptide. It is oligomeric and acidic (an excess of nine negative charges). It does not contain Phe, Trp, Tyr, His, Pr o, and Cys. Only 25 N-terminal residues were still able to complement a g57 amber mutant, although with a reduced efficiency. In cells overp roducing the protein, it assumed a quasi-crystalline structure in the form of highly ordered fibers. They traversed the cells longitudinally (and thus blocked cell division) with a diameter approaching that of the cell and with a hexagonal appearance. The 194-residue pTfa is also acidic (an excess of 13 negative charges) and is likely to be dimeric .