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Proceedings: Molecular aspects of gene regulation in animal cells.

Gene regulation in animal cells may occur at several stages of RNA metabolism, including synthesis, processing, transport, and utilization of the RNA. This discussion primarily concerns transcription level regulation, i.e., control over which sequences in the genomic DNA are transcribed. Current evidence indicates that this is the initial level of regulation in the differentiated animal cell; this conclusion is supported by quantitative hybridization experiments as well as by other kinds of data. Recent experiments are considered which show that animal structural genes are in general DNA sequences occurring only once per haploid genome. For at least one system, the sea urchin embryo, the amount of nonrepetitive DNA sequence represented in the mRNA's is known. About 14,000 average-sized structural genes are represented in the polysomal mRNA of this 600-cell embryo. Studies on organization of DNA sequences show that at least 80% of the DNA of Xenopus and sea urchin consists of short (300 nucleotides) repetitive sequence elements interspersed with longer nonrepetitive sequence regions. This arrangement is an ordered one, suggesting selective value in evolution and therefore function. Such a sequence arrangement pattern could account for the system properties of gene regulation in animal cells.