The finger motif defines a multigene family represented in the maternal mRNA of Xenopus laevis oocytes.

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We have screened Xenopus laevis cDNA and genomic libraries for finger motif encoding sequences by use of a synthetic oligonucleotide probe coding for a stretch of conserved amino acids, the H/C-link, which joins individual finger loops in several multi-fingered proteins. Our studies reveal that a large number of different cDNA clones encode amino acid sequences predicting multiple units of the metal-coordinating finger structure. Derived proteins are different from each other as well as from the two examples of Xenopus finger proteins reported to date, TFIIIA and X.fin. The 109 finger repeats characterized are derived from 14 different cDNA clones and have been analysed for the presence of conserved and highly variable amino acids, revealing a close structural relatedness among each other as well as with a few selected finger domains from Drosophila and mouse proteins. The results from this comparative sequence analysis are also discussed in terms of the existing models for DNA binding. All sequences are identified in an ovary cDNA library but the patterns of mRNA level for individual finger clones vary greatly during early development. The prevalence of these structures in the oocyte suggests that part of the maternal information for the realization of the developmental program utilized in Xenopus embryogenesis might be transmitted in the form of regulatory, nucleic-acid-binding proteins.

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