Biosynthesis and secretion of insect lipoprotein: involvement of furin in cleavage of the apoB homolog, apolipophorin-II/I.

The biosynthesis of neutral fat-transporting lipoproteins involves the lipidation of their nonexchangeable apolipoprotein. In contrast to its mammalian homolog apolipoprotein B, however, insect apolipophorin-II/I (apoLp-II/I) is cleaved posttranslationally at a consensus substrate sequence for furin, resulting in the appearance of two apolipoproteins in insect lipoprotein. To characterize the cleavage process, a truncated cDNA encoding the N-terminal 38% of Locusta migratoria apoLp-II/I, including the cleavage site, was expressed in insect Sf9 cells.

Rat B-50 gene transcription and translation.

Previously we reported that the rat B-50/GAP-43 gene contains two promoters (P1 and P2). This study describes the contribution of these two promoters to the mRNA population in several paradigms leading to an altered B-50 mRNA expression. In 8-day-old rat brain we found that P1 transcripts (1676 +/- 50 nt) account for 5% and P2 transcripts (1462 +/- 46 nt) for 95% of the B-50 mRNAs.

The amino acid sequence of eukaryotic translation initiation factor 1 and its similarity to yeast initiation factor SUI1.

Eukaryotic initiation factor eIF-1 was purified from rabbit reticulocytes. Amino acid sequence analysis revealed that the protein contained a blocked amino-terminus. After cleavage with the endoproteinase Asp-N, three peptides were sequenced.

Translation initiation on the insulin-like growth factor II leader 1 is developmentally regulated.

The majority of cellular mRNAs have relatively short and unstructured 5' untranslated regions (UTRs) that allow efficient translation, such as the beta-globin mRNA. An exception to this rule is the group of growth factor mRNAs which, in general, have long 5' UTRs with a high G + C content. An example is insulin-like growth factor II (IGF-II), which is encoded by four mRNAs, arising from four different promoters.

Epidermal growth factor stimulates phosphorylation of eukaryotic initiation factor 4B, independently of protein kinase C.

We demonstrate that exposure of human epidermoid carcinoma A431 cells to epidermal growth factor (EGF) results in phosphorylation of eIF-4B within minutes after addition of EGF. The EGF-induced phosphorylation of eIF-4B is not caused by the EGF receptor tyrosine kinase itself, since no tyrosine-phosphorylated eIF-4B could be detected upon immunoprecipitation using an anti-phosphotyrosine antibody. Enhanced phosphorylation of eIF-4B was also detected upon exposure of the cells to phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), suggesting that eIF-4B may be a substrate of PKC.