Premature processing of mouse mammary tumor virus Gag polyprotein impairs intracellular capsid assembly

Mouse mammary tumor virus (MMTV) is the prototypical member of the Betaretrovirus genus, but the processes of its morphogenesis are poorly characterized. In this report, we describe an unusual intracellular processing of MMTV Gag polyprotein in human 293T cells transiently expressing MMTV from heterologous promoter. The same specific cleavage products of the viral protease were seen for the wild type as well as for nonmyristylated mutant of MMTV Gag polyprotein completely defective in the particle release. Inactivation of the viral protease resulted in more stable Gag polyprotein and in accumulation of intracytoplasmic particles for nonmyristylated Gag. The intracellular processing of nonmyristylated MMTV Gag indicates that protease activation in betaretrovirus can occur independently of budding.     

Localization of self-interacting domains within betaretrovirus Gag polyproteins

The Betaretrovirus genus is characterized by the ability to preassemble immature capsids within the cytoplasm. For Mason-Pfizer monkey virus (M-PMV) this ability depends in part upon the unique Internal Scaffold Domain (ISD) within the p12 region of Gag. In this study, we have further characterized the ability of M-PMV p12 to promote Gag-Gag interaction and have examined the Gag polyprotein of the related mouse mammary tumor virus (MMTV) to potentially identify a region with equivalent function. Using the yeast two-hybrid system, we confirmed that both Gag polyproteins strongly interact, primarily through the CA-NC regions, but also through additional domains N-terminal to CA. For M-PMV, this auxiliary interaction domain was p12. For MMTV, no single strongly self-interacting protein was identified. Instead, MMTV Gag appears to utilize the weak contributions of several protein domains to support the main interaction of its CA-NC. Our findings suggest that, in addition to the canonical NC "I-domain" interaction, MMTV Gag self-association results from the concerted action of multiple regions of the polyprotein while M-PMV Gag relies mainly on its p12 domain.     

Detection and characterization of betaretroviral sequences, related to sheep Jaagsiekte virus, in Africans from Nigeria and Cameroon

Jaagsiekte retrovirus (JSRV) causes ovine pulmonary adenomatosis (OPA) that resembles bronchioloalveolar carcinoma (BAC) in humans. To test the possible role of JSRV in human diseases, DNA specimens from 103 individuals either healthy or suffering from lung carcinomas were analyzed for JSRV sequences. orf-x sequences were detected in 19 of 64 samples and gag-prt sequences in 4 of 38 samples, predominantly in individuals from Africa. Sequences obtained from orf-x amplimers varied in-between each other and differed from control endogenous ovine JSRV sequence. No association with lung cancer was found. This is the first report of JSRV-like sequences detected in humans.     

Conservation of inner domain modules in the surface envelope glycoproteins of an ancient rabbit lentivirus and extant lentiviruses and betaretroviruses

The consensus sequence of endogenous lentiviral elements in the genome of European rabbits (RELIK) was used to extend a model of conserved lentiviral and betaretroviral surface envelope glycoprotein (SU) inner domain structures. Here it is shown that nearly all the inner domain elements of human and simian immunodeficiency virus gp120 mediating conformational changes upon CD4 binding were conserved in the SU of RELIK. Many of these inner domain elements and a carboxy-terminal region outside the gp120 core are also conserved in the SU of other lentiviruses and betaretroviruses, suggesting conserved mechanisms of SU conformational changes induced by receptor binding.     

猴D型反转录病毒巢式PCR检测方法的建立

目的建立SRV-1巢式PCR检测方法并进行初步应用。方法针对SRV-1env基因的保守区序列,设计特异性引物,以感染SRV-1 Raji细胞提取出的含有前病毒DNA的基因组DNA为模板,进行巢式PCR反应。扩增产物测序后与GenBank报道的序列进行同源比对。将DNA样本进行10倍梯度稀释,以检测巢式PCR反应的灵敏度。使用该方法对正常Raji细胞以及感染SIV、STLV的外周血淋巴细胞DNA样本进行扩增,检测该方法的特异性。用建立的巢式PCR方法检测40份储存猴血标本。结果使用巢式PCR扩增出的特异片段经测序分析,结果证实与GenBank报道的序列一致。所建立的巢式PCR检测法检测限度可达1.5×10-3ng/μL,而且方法特异。用此方法检测40份猴血标本,未检测到阳性标本。结论初步建立SRV-1的巢式PCR检测方法,该方法灵敏、特异,为SRV-1的检测提供了一个快速、有效的手段。