Role of the major capsid protein of phage T4 in DNA packaging from structure-function and site-directed mutagenesis studies.
Heat cleavage of asp-pro peptide bonds was used to probe the primary structures of the Phage T4 major capsid protein precursor, gp23, its mature capsid form gp23*, and a DNA-dependent ATPase, called capsizyme. This analysis suggests that capsizyme is a gp23** resulting from the N-terminal processing found in gp23* as well as shortening at the C-terminus. Photoaffinity labeling with Azido-ATP and BrU-DNA, followed by heat cleavage, suggests binding sites for these compounds toward the C-terminus of gp23**, suggesting localization of functions within the gp23 primary sequence. Site-directed mutagenesis experiments were targeted therefore to the C-terminal end of g23 as well as to its processing sites. N-terminal processing site modification supports the consensus gp21 proteinase cleavage rule, whereas mutagenesis at the C-terminus suggests that the C-terminal alteration is unlikely to result from a gp21-morphogenesis proteinase cleavage. Amino acid replacements in gp23 at newly introduced amber sites reveal a new g23 mutant phenotype, defective partially DNA-filled heads, in support of the hypothesis that gp23 and its products function directly in the DNA packaging mechanism.
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Department of Biological Chemistry, University of Maryland Medical School, Baltimore 21201.
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D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002213:Capsid / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D036022:Capsid Proteins; D004279:DNA, Viral / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015345:Oligonucleotide Probes; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D013604:T-Phages / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
D036022:Capsid Proteins; D004279:DNA, Viral; D015345:Oligonucleotide Probes; D011498:Protein Precursors; C064517:gp23 protein, Bacteriophage T4; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases