No abstract

We present the sequence of the nuclear-encoded ribosomal small-subunit RNA from soybean. The soybean 18S rRNA sequence of 1807 nucleotides (nt) is contained in a gene family of approximately 800 closely related members per haploid genome. This sequence is compared with the ribosomal small-subunit RNAs of maize (1805 nt), yeast (1789 nt), Xenopus (1825 nt), rat (1869 nt), and Escherichia coli (1541 nt). Significant sequence homology is observed among the eukaryotic small-subunit rRNAs examined, and some sequence homology is observed between eukaryotic and prokaryotic small-subunit rRNAs. Conserved regions are found to be interspersed among highly diverged sequences. The significance of these comparisons is evaluated using computer simulation of a random sequence model. A tentative model of the secondary structure of soybean 18S rRNA is presented and discussed in the context of the functions of the various conserved regions within the sequence. On the basis of this model, the short base-paired sequences defining the four structural and functional domains of all 18S rRNAs are seen to be well conserved. The potential roles of other conserved soybean 18S rRNA sequences in protein synthesis are discussed.

We have investigated the actin-related sequences in soybean using heterologous actin DNA probes from Dictyostelium, Drosophila, and yeast. Southern blot analysis of restriction digests of soybean DNA indicates that actin is encoded in a small multigene family. In order to isolate individual members of this gene family, we have constructed a soybean genomic library in the lambda vehicle Charon 4A. A partial characterization of this library shows it to be nearly complete. We have isolated from this library a number of recombinant clones that hybridize to actin-coding sequences from all three heterologous probes. We have identified the fragments containing the actin-related sequences on the physical maps of two of these clones lambda SAc1 and lambda SAc3. These fragments were subcloned in the plasmid vehicle pBR322. Using electron microscope heteroduplex mapping we show that the subclones, pSAc1 and pSAc3, share homology with the entire actin-coding sequence (1.1 kb) of Drosophila and Dictyostelium. Furthermore, pSAc1 and pSAc3 have additional homology of approximately 0.22 kb at the 5' ends of their coding sequences. No homology is detected in the 3' flanking regions of these clones. The actin sequence in pSAc1 contains an interruption of approximately 0.30 kb located 0.39 kb from the 5' end of the actin polypeptide coding region.

No abstract

No abstract