Analysis of secondary modifications of mouse mammary tumor virus proteins by two-dimensional gel electrophoresis

Abstract

The structural proteins of mouse mammary tumor virus (MMTV) were analyzed by two-dimensional electrophoresis on isoelectric focusing and sodium dodecyl sulfate gels. Many of the viral proteins displayed heterogeneity in charge due to variable contents of carbohydrates (in particular, sialic acid) and phosphate residues. Neuraminidase treatment ofthe virions influenced the isoelectric pattern of the envelope glycoproteins. The glycoproteins of an MMTV variant which was attenuated by replication in feline kidney cells had different isoelectric points. This suggested that the acquisition of an altered carbohydrate configuration had changed the host range of the virus. The major MMTV structural core protein, p27, consisted of two species, which had identical iodinated tryptic peptide compositions but differed in phosphate contents. Another MMTV phosphoprotein, p21, was separated into four different phosphorylated species. Phosphorylation of p21 could be performed in vitro by the MMTV virion-associated protein kinase. This enzyme also has a high affinity for MMTV p30. as a substrate. Possible functions of this enzyme are discussed.

Analysis of gag proteins from mouse mammary tumor virus

“…2, lane 3). Subsequent analysis (see below) showed that peak a contained a gag protein that was probably the viral gag phosphoprotein previously referred to as pp2l (4,26,27,33). Protein eluting in peak b (Fig.…”

CrFK Feline Kidney Cells Produce an RD114-Like Endogenous Virus That Can Package Murine Leukemia Virus-Based Vectors

“…CrFK feline kidney cells have been used extensively both to propagate and to investigate the biology of a number of enveloped viruses, including retroviruses such as feline immunodeficiency virus (FIV) (1,2,6,19,21,27,32), feline leukemia virus (FeLV) (23), mouse mammary tumor virus (MMTV) (13,20,24), herpesviruses (7,35), coronaviruses (3,12), and feline syncytial virus (18). Further, retrovirus vectors based on MMTV (4,25) and FIV (22) have been constructed with CrFK cells.…”

“…Also, much of the biology of FIV, and to some extent MMTV, has been elucidated with CrFK cells. Indeed, CrFK is one of the few cell lines known to be permissive for production of MMTV (13,20,24). Although it is not clear whether the CrLE virus can act as a helper for FIV or type B viruses, the formation of pseudotypes may also contribute to infection (33).…”

Immunoelectron Microscopic Localization of Mammary Tumor Virus (MTV) Antigens in Normal and Cancerous Mammary Glands of Mice

“…The endoplasmic reticulum seems to play an important role in the synthesis and transport of the MTV envelope antigen. The cell fractionation studies (4,11) indicated that this protein migrated from membrane-bound ribosomes to the plasma membrane via the smooth endoplasmic reticulum and the Golgi apparatus. The staining of these cytoplasmic vesicular structures was not homogeneous in individual cells.…”

“…The major envelope protein, gp52, is glycosylated. Glycosylation of the precursor protein of gp52 occurs on membrane-bound ribosomes during its transport through the endoplasmic reticulum to the plasma membrane (4,11). Intracytoplasmic…”