Within the first hour of zygote maturation, Chlamydomonas reinhardtii cells stop synthesizing certain polypeptides that characterize the vegetative and gametic stages of the life cycle and initiate the synthesis of novel, zygote-specific polypeptides. At least six of these polypeptides are secreted into the medium, and fine-structural studies indicate that they represent components of the cell wall that is synthesized and secreted early in zygote development. We conclude that a new program of protein synthesis, and possibly also gene transcription, is initiated shortly after gametic cells fuse, a program that appears highly suited to cell-differentiation studies.

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