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The auxin-regulated expression of two poly(A)+ mRNAs in soybean hypocotyl was demonstrated by cloning of the cDNAs and Northern blot hybridization analyses (Walker, J.C., and Key, J.L. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 7185-7189). The corresponding genes, designated Aux28 and Aux22, have been isolated, and the cDNAs and genes have been sequenced. The Aux28 and Aux22 genes are present at one to two copies per haploid genome, contain four and two introns, and encode hydrophilic proteins of 26.8 and 21.5 kDa, respectively. Although the cDNAs were isolated independently and do not cross-hybridize under stringent hybridization conditions, the protein coding sequences of the two cDNAs have several colinear regions of high homology at the nucleic acid (77-80%) and the amino acid (80-100%) levels; together these regions constitute approximately a third of the protein coding sequences of the cDNAs. These data, together with genomic Southern blot hybridization analysis and hybrid-select translations of mRNAs homologous to the cDNAs, show that these genes belong to two related multigene families. We have identified two sequences, TGATAAAAG and GGCAGCATGCA, that occur at similar distances upstream of the transcription start site in each gene, and the spacing between these two elements is essentially identical in the two genes. The possible significance of these sequences is under evaluation. |
