Observations on Steganacarus magnus: differences between the instars.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
N R Webb
Publications and source records attributed to N R Webb.
Cloning and sequence analysis of a cDNA for rat transforming growth factor-alpha.
Transforming growth factors (TGFs) are mitogenic polypeptides produced most conspicuously by transformed cells and conferring on normal cells several phenotypic alterations associated with transformation. TGFs comprise two distinct sets of molecules: TGF-alpha s are structurally similar to epidermal growth factor (EGF), binding to and inducing the tyrosine phosphorylation of the EGF receptor in a manner indistinguishable from that of EGF. In addition, the 50-amino acid rat TGF-alpha has 33 and 44% homologies with mouse and human EGFs, respectively, and shares with EGFs a conserved pattern of three disulphide bridges. Thus, it has been proposed that TGF-alpha s belong to a family of EGF-like polypeptides. TGF-beta s, on the other hand, display no measurable binding to EGF receptors, but potentiate the growth-stimulating activities of TGF-alpha. Here we report the isolation of a complementary DNA clone encoding rat TGF-alpha. This cDNA hybridizes to a 4.5-kilobase (kb) messenger RNA that is 30 times larger than necessary to code for a 50-amino acid polypeptide and is present not only in retrovirus-transformed rat cells but also at lower levels in normal rat tissues. The nucleotide sequence of the cDNA predicts that TGF-alpha is synthesized as a larger product and that the larger form may exist as a transmembrane protein. However, unlike many polypeptide hormones (including EGF), cleavage of the 50-amino acid TGF-alpha from the larger form does not occur at paired basic residues, but rather between alanine and valine residues, suggesting the role of a novel protease.
Animals↗
Transforming growth factor-beta 2: cDNA cloning and sequence analysis.
We have obtained a cDNA clone coding for human transforming growth factor (TGF)-beta 2. The clone was isolated from a tamoxifen-treated human prostatic adenocarcinoma cell line (PC-3) using oligonucleotide probes based on the partial amino acid sequence of purified TGF-beta 2. The cDNA sequence predicts that TGF-beta 2 is synthesized as a 442-amino-acid polypeptide precursor from which the mature 112-amino-acid TGF-beta 2 subunit is derived by proteolytic cleavage. The proteins coded for by the human TGF-beta 1 and TGF-beta 2 cDNAs show an overall homology of 41%. The mature and amino-terminal precursor regions show 71% and 31% homology, respectively. Northern blot analysis identified TGF-beta 2 transcripts of 4.1, 5.1, and 6.5 kb using mRNA from several different sources. Analysis of polyadenylated RNA from tamoxifen-treated PC-3 cells showed that these cells contain higher numbers of transcripts for TGF-beta 1 than for TGF-beta 2, although they produce more TGF-beta 2 protein than TGF-beta 1. This suggests that there is a post-transcriptional level of regulation for the production of these proteins.
Amino Acid Sequence↗