Separation of the mRNAs coding for different forms of chick embryo gizzard tropomyosin

The fractionation of gizzard tropomyosin from 17-day-old chick embryos by electrophoresis in polyacrylamide gels indicates that this protein is composed of three different polypeptides that were designated as alpha, beta, and gamma. Each one of these polypeptides is resolved into two components with different isoelectric points when tropomyosin is fractionated by two-dimensional electrophoresis; the major components were designated as tropomyosins alpha 1, beta 1, and gamma 1 and the minor ones as tropomyosins alpha 2, beta 2, and gamma 2. The results of in vitro translation of gizzard RNA indicate that only tropomyosins alpha 1, beta 1, and gamma 1 are synthesized in the cell-free system. A partial separation of the mRNAs coding for tropomyosins alpha 1 and gamma 1 was obtained by fractionation of gizzard RNA by zonal centrifugation in sucrose gradients. Altogether these results indicate that in gizzard tissue from 17-day-old chick embryos three genes coding for different forms of tropomyosin are expressed.