The chorionic gonadotropin β (CGβ) subunit is encoded by a multigene cluster composed of six homologous sequences (genes or pseudogenes). They are primarily distinguished by sequences in the 5' nontranslated region of the first exon. To determine which CGβ genes are active in vivo, we employed the reverse transcription-polymerase chain reaction technique. DNA complementary to RNA from placenta tissue and a choriocarcinoma cell line was subjected to polymerase chain reaction with CGβ-specific primers. The amplified DNA was cloned into M13 and sequenced. Most of steady-state CGβ mRNAs are transcribed from CGβ genes, 5, 3, and 8. The level of expression is β5 > β3 = β8 > β7, β1/2. Transcripts from the CGβ1 and CG 1/2 genes, which were previously considered pseudogenes because of their noncanonical splice site, were detected. These CGβ transcripts arising from alternative splicing sites in the CGβ1/2 genes were also detected in polysomes which suggests they are translation-competent. Northern blotting with a CGβ1/2 probe revealed low amounts of CGβ1/2 transcripts which were smaller than the transcripts of the other genes. The results indicate that at least five, and possibly all six, CGβ genes are transcribed in vivo, and at least one of them (CGβ1 and/or CGβ2) undergoes alternative splicing.
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - Jan 1 1992|