Balvay L, Fiszman M Y
INSERM U 153, Groupe Hospitalier Pitié-Salpêtrière, Paris.
C R Seances Soc Biol Fil. 1994;188(5-6):527-40.
Tropomyosins are a family of actin filament binding proteins. Like many structural proteins, tropomyosin isoform expression involves the use of multiple genes, but diversity is to a large extent generated by alternative processing of RNA. The tropomyosin family consists of 15 to 20 different protein isoforms which are coded by four genes. Each of these genes code for multiple proteins ranging from two up to as many as nine different isoforms. These genes have been named alpha CTM, alpha FTM, alpha STM and beta TM after to the striated muscle specific subunit of tropomyosin which they code. Their multiple coding potential is based upon the existence of multiple exons associated with initiation of transcription, multiple exons associated with polyadenylation signals and multiple mutually exclusive internal exons which are alternatively spliced. The regulation of this process of alternative splicing have been extensively studied both in the case of exons 2a/2b of the alpha FTM gene and in the case of exons 6a/6b of the beta TM gene. In both cases, one exon is specifically used in one type of muscle tissue, exon 2a is smooth muscle specific and exon 6b is skeletal muscle specific. In both cases, alternative splicing involves a combination of negative regulation, on exon 2b in smooth muscle and on exon 6b in non muscle tissues, and of competition in the alternative situation.
原肌球蛋白是一类肌动蛋白丝结合蛋白。与许多结构蛋白一样，原肌球蛋白同工型的表达涉及多个基因的使用，但多样性在很大程度上是由RNA的可变加工产生的。原肌球蛋白家族由15至20种不同的蛋白质同工型组成，它们由四个基因编码。这些基因中的每一个都编码多种蛋白质，从两种到多达九种不同的同工型。这些基因根据它们编码的原肌球蛋白的横纹肌特异性亚基分别命名为αCTM、αFTM、αSTM和βTM。它们的多重编码潜力基于与转录起始相关的多个外显子、与聚腺苷酸化信号相关的多个外显子以及多个相互排斥的内部外显子的存在，这些外显子可选择性剪接。在αFTM基因的外显子2a/2b以及βTM基因的外显子6a/6b的情况下，都对这种可变剪接过程的调控进行了广泛研究。在这两种情况下，一种外显子在一种类型的肌肉组织中被特异性使用，外显子2a是平滑肌特异性的，外显子6b是骨骼肌特异性的。在这两种情况下，可变剪接都涉及负调控的组合，即在平滑肌中的外显子2b和非肌肉组织中的外显子6b上，以及在可变情况下的竞争。
