Quantification of the DNA Cleavage and Packaging Proteins UL15 and UL28 in A and B Capsids of Herpes Simplex Virus Type 1

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American Society for Microbiology

RESUMO

The proteins produced by the herpes simplex virus type 1 (HSV-1) genes UL15 and UL28 are believed to form part of the terminase enzyme, a protein complex essential for the cleavage of newly synthesized, concatameric herpesvirus DNA and the packaging of the resultant genome lengths into preformed capsids. This work describes the purification of recombinant forms of pUL15 and pUL28, which allowed the calculation of the average number of copies of each protein in A and B capsids and in capsids lacking the putative portal encoded by UL6. On average, 1.0 (±0.29 [standard deviation]) copies of pUL15 and 2.4 (±0.97) copies of pUL28 were present in B capsids, 1.2 (±0.72) copies of pUL15 and 1.5 (±0.86) copies of pUL28 were found in mutant capsids lacking the putative portal protein pUL6, and approximately 12.0 (±5.63) copies of pUL15 and 0.6 (±0.32) copies of pUL28 were present in each A capsid. These results suggest that the packaging machine is partly comprised of approximately 12 copies of pUL15, as found in A capsids, with wild-type B and mutant UL6(−) capsids containing an incomplete complement of cleavage and packaging proteins. These results are consistent with observations that B capsids form by default in the absence of packaging machinery in vitro and in vivo. In contrast, A capsids may be the result of initiated but aborted attempts at DNA packaging, resulting in the retention of at least part of the DNA packaging machinery.

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