Search

In order to examine the control of human factor X biosyn thesis we have molecularly cloned the cDNA and investi gated the expression of the Factor X gene. A recombinant clone of approximately 1100 base pairs in length containing the sequence of factor X was identified in a Xgt11 human liver cDNA library by screening with polyclonal antibodies. One plaque was selected and confirmed for specificity with a mixture of five factor X specific monoclonal antibodies (MoAbs). A partial nucleic acid sequence of the 5' end of the cDNA corresponded to the described amino acid sequence between residues 41 and 56 of the light chain of factor X. Northern blot analysis of RNA from human liver and the hepatoma cell line. Hep G2, identified the factor X mRNA as a single molecular species of approximately 1700 bases. Cell lines which do not secrete factor X did not contain factor X mRNA indicating restriction of tran scription to hepatocytes. Slot-blot hybridization analysis of factor X and actin mRNA demonstrated no change in the levels of total or specific factor X mRNA in Hep G2 cells following treatment with warfarin or vitamin K. We con clude that modulation of factor X production by these drugs, known to influence 7-carboxylation and total factor X secretion by these cells, is mediated by changes in posttranscriptional events rather than by effects on the steady state levels of factor X mRNA.

A major murine mammary tumor viral (MMTV) antigen, sl, originally described by Nowinski et al. (1967, 1968, 1971), has been purified from RIII mouse milk MMTV by sequential ion-exchange and gel chromatography. The purified protein with sl antigenic reactivity contains carbohydrate, and has an apparent minimal molecular weight of 52,000. It can be designated as gp52 (sl). Another major MMTV viral protein with a molecular weight of 27,000 has also been isolated, and antisera have been prepared against it. Both MMTV gp52 (sl) and p27 viral polypeptides have been iodinated with 125I and used in immunoprecipitation and competition assays. The two MMTV proteins differ absolutely from each other and from major mouse type C viral polypeptides in molecular weight, immunological reactivity, and amino acid composition. Purified gp52 (sl) in radioimmunoprecipitation inhibition assays reacted in two distinct patterns. One pattern showed partial displacement of antibody which could be converted to the second, a complete displacement, by heating the antigen, presumably by exposing additional reactive determinants. Biologically, the patterns of major MMTV polypeptide expression in milk correlated with spontaneous mammary tumor incidence in different strains of mice, indicating that the sl antigen is group specific for MMTV or that several mouse strains contain the same virus type.