Characterization of muscle and non muscle Xenopus laevis tropomyosin mRNAs transcribed from the same gene

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Abstract
We have isolated and characterized three Xenopus laevis tropomyosin cDNAs (XTMα2, XTMα4 and XTM05). XTMα2 and XTMα4 were isolated from a stage-42 embryo cDNA library and XTM05 from an oocyte cDNA library. XTMα2 and XTMα4 both code for a 284-amino-acid protein homologous to the skeletal α tropomyosin but diverge in their 3′ untranslated sequences. This divergence is due to an absence of splicing in the early embryo. XTM05 codes for a 248-amino-acid non-muscle tropomyosin. Sequence analysis indicates that the three cDNAs are generated from a single gene which uses two promoters and possibly three sets of alternate exons. Northern blot analysis, with specific probes against each cDNA, was used to study the expression of the X. laevisα tropomysin gene during development and in specific tissues. This analysis showed a different temporal usage of the two promoters and characterized the tissue-specific expression of the different transcripts.