TEMPERATURE-SENSITIVE MUTANTS BLOCKED IN THE FOLDING OR SUBUNIT ASSEMBLY OF THE BACTERIOPHAGE-P22 TAIL-SPIKE PROTEIN .1. FINE-STRUCTURE MAPPING

  • 1 January 1980
    • journal article
    • research article
    • Vol. 96  (2) , 331-352
Abstract
As part of a study of protein folding, a fine-structure map was constructed of 9 existing and 29 newly isolated UV- and hydroxylamine-induced temperature-sensitive (ts) mutations in gene 9 of Salmonella bacteriophage P22. Gene 9 specifies the polypeptide chain of the multimeric tail spikes, 6 of which form the cell attachment organelle of the phage. The 38 ts mutants were mapped against deletion lysogens with endpoints in gene 9. They mapped in 10 of the 15 deletion intervals. Two- and 3-factor crosses between mutants within each interval indicated that at least 31 ts sites are represented among the 38 mutants. To determine the distribution of ts sites within the physical map, the protein fragments from infection of su- hosts with 10 gene 9 amber mutants were identified. Their MW, ranging from 13,900-55,000 daltons, were combined with the genetic data to yield a composite map of gene 9. The 31 ts sites were distributed through most of the gene, but were most densely clustered in the central third. None of the ts mutant pairs tested exhibited intragenic complementation. Previous studies of the defective phenotypes of the ts mutants revealed that most do not affect the thermostability of the mature protein, but instead prevent the folding or subunit assembly of the mutant chains synthesized at restrictive temperature. Thus, many ts mutations identify sites in the polypeptide chain that are critical for the folding or maturation of the tail-spike protein.