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Previous studies have revealed critical roles for the human cytomegalovirus (HCMV) UL97 kinase in viral nuclear maturation events. We have shown recently that UL97 affects the morphology of the viral cytoplasmic assembly compartment (AC) (M. Azzeh, A. Honigman, A. Taraboulos, A. Rouvinski, and D. G. Wolf, Virology 354:69-79, 2006). Here, we employed a comprehensive ultrastructural analysis to dissect the impact of UL97 on cytoplasmic steps of HCMV assembly. Using UL97 deletion (⌬UL97) and kinase-null (K355M) mutants, as well as the UL97 kinase inhibitor NGIC-I, we demonstrated that the loss of UL97 kinase activity resulted in a unique combination of cytoplasmic features: (i) the formation of pp65-rich aberrant cytoplasmic tegument aggregates, (ii) distorted intracytoplasmic membranes, which replaced the normal architecture of the AC, and (iv) a paucity of cytoplasmic tegumented capsids and dense bodies (DBs). We further showed that these abnormal assembly intermediates did not result from impaired nuclear capsid maturation and egress per se by using 2-bromo-5,6-dichloro-1-(␤-d-ribofuranosyl) benzimidizole (BDCRB) to induce the artificial inhibition of nuclear maturation and the nucleocytoplasmic translocation of capsids. The specific abrogation of UL97 kinase activity under low-multiplicity-of-infection conditions resulted in the improved release of extracellular virus compared to that of ⌬UL97, despite similar rates of viral DNA accumulation and similar effects on nuclear capsid maturation and egress. The only ultrastructural correlate of the growth difference was a higher number of cytoplasmic DBs, tegumented capsids, and clustered viral particles observed upon the specific abrogation of UL97 kinase activity compared to that of ⌬UL97. These combined findings reveal a novel role for UL97 in HCMV cytoplasmic secondary envelopment steps, with a further distinction of kinase-mediated function in the formation of the virus-induced AC and a nonkinase function enhancing the efficacy of viral tegumentation and release.Human cytomegalovirus (HCMV), a ubiquitous betaherpesvirus, is a major cause of disease in immunocompromised individuals and a leading cause of congenital infection (57). The HCMV virion consists of a DNA-containing capsid, which is embedded in a tegument layer, and a lipid envelope, which contains the virus-encoded glycoproteins (57). The HCMV infection of cells in culture generates infectious virions, as well as dense bodies (DBs; nonreplicating particles composed of tegument surrounded by an envelope) and noninfectious enveloped particles lacking viral DNA (57, 80).During capsid maturation in the nucleus, large concatemeric DNA intermediates are cleaved to genome-length units and packaged into preformed capsids via the DNA cleavage/packaging machinery (57). The current model suggests that assembled nucleocapsids bud through the inner nuclear membrane, acquiring a primary envelope layer. Subsequent shuttling into the cytoplasm and cytoplasmic assembly steps involve deenvelopment and the budding of nucl...

Histamine insolubilized by chemical linkage via a protein or polypeptide carrier to Sepharose beads cannot penetrate cells. Even so, the resultant histamine-coated Sepharose binds leukocytes selectively. Despite the low molecular weight of histaminie, the binding is via preformed cell membrane receptors and can be specifically and competitively blocked or reversed by antihistamines.

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