Title: Splicing of the alternative exons of the chicken, rat, and Xenopus beta tropomyosin transcripts requires class-specific elements.
Abstract: The diversity of protein isoforms is often generated from single genes by alternative splicing of the primary transcript.Using transfection of fi tropomyosin minigene constructs into homologous and heterologous cell systems, we show that there are differences, among higher vertebrates, in the components of the splicing machinery which control the conserved regulated splicing pattern of two mutually exclusive exons (6A and 6B) present in this gene.These experiments demonstrate that genes which give rise to alternative transcripts may require an appropriate combination of splicing factors which are species-specific, or at least restricted to the same taxonomic subgroup (class).A n important practical implication is that the splicing of these genes may be deregulated in heterologous systems in vitro and in uiuo, i.e. in transgenic animals.The molecular characterization of an increasing number of eukaryotic genes in the last decade has revealed that alternative splicing, by which a single gene has the capacity to encode multiple protein products, is a fundamental mode of genetic control (1, 2).The splicing pattern generated from such genes can be extremely complex and is often regulated in a tissue-or a developmental-specific manner, so that the choice of a particular pattern can reflect the differentiated state of the cell (3).Important advances in studying the mechanisms involved in constitutive and alternative pre-mRNA splicing have been made by using cellular transfections and HeLa nuclear extracts