Molecular cloning and sequence determination of four different cDNA species coding for α‐subunits of G proteins from Xenopus laevis oocytes

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Abstract
A cDNA library preprared from Xenopus laevis oocytes in λgt10 was screened with a mixture of three oligonucleotide probes designed to detect sequences found in different mammalian genes coding for a-subunits of G-proteins. In addition to a clone coding for a Gαo-type subunit previously reported [(1989) FEBS Lett. 244, 188-192] four additional clones have been found coding for different Gα protein subunits. By comparison with mammalian α-subunits, these oocyte cDNAs correspond to two closely related Gas-la, to a Gαi-1 and to a Gαi-3 species. The derived amino acid sequences showed that both Gαs species contain 379 residues, corresponding to the short species without the serine residue and with a calculated M r of 42720. The Gαi-1 gene encodes a 354 amino acid protein with an M r, of 39000 and the Gαi-3 encodes an incomplete open reading frame of 345 residues, lacking the first 9 amino acid residues at the NH2, terminus. All these Gα-subunits showed high identity with their respective mammalian counterparts (75–80%), indicating a great degree of conservation through the evolution and the important cellular regulatory function that they play.