THE POLYHEDRA OF THE OCCLUDED BACULOVIRUSES OF MARINE DECAPOD CRUSTACEA - A UNIQUE STRUCTURE, CRYSTAL ORGANIZATION, AND PROPOSED MODEL

The baculoviruses of marine penaeid shrimp, PmSNPV and PvSNPV (MBV typ e and BP type, respectively), have distinctly different occlusion bodi es (OBs) from those of the insect baculoviruses. In contrast to insect baculovirus, the penaeid baculovirus OB is unenveloped and formed by large subunits (SuOBs), as observed by electron microscopy after negat ive staining. The polyhedrin subunits measure 17 to 23 nm in diameter and appear icosahedral, resembling full and empty viral particles. Alt hough these SuOBs look similar in morphometrics to shrimp parvoviruses , their density, polypeptide composition, and UV spectra are more char acteristic of proteins than nucleoproteins. Common to the two shrimp b aculovirus OBs that were investigated is the aggregation of three icos ahedral SuOBs into a triplet. The observed difference in their crystal line structure is directly related to the way in which triplets attach to each other to form the OB. In the BP-type OB, the triplets form al ternating parallel rows in all three dimensions. On the other hand, in the MBV-type OB, four triplets form a hollow sphere which we call a ' 'rosette,'' the building blocks of the MBV-type OB. We assembled model s for the penaeid baculovirus OB as an alternative to those hypothesiz ed for insect baculovirus OBs. (C) 1997 Academic Press.