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These descriptive findings during the standing and sitting skiing protocols provide preliminary data that would be useful in testing, training, and classification of competitive skiers with disabilities.

We have used two approaches to search for sequence variants in the 18S coding region of amplified ribosomal DNA (rDNA) from Xenopus laevis oocytes. First, using clones derived from amplified rDNA, we compared the equivalent of a complete 18S coding region from two clones and short regions from two other clones with the 18S sequence previously determined from a “reference” clone. The respective sequences in all the clones were identical. Secondly, we examined greater than 60% of the 18S sequence in “pooled 18S genes” in uncloned amplified rDNA. The predominant sequence corresponded to that in the reference clone and no heterogeneities were apparent. Since many chromosomal rDNA units contribute to rDNA amplification the findings indicate that 18S coding sequences in X. laevis are largely homogeneous. The previously established sequence is the predominant one, thus providing a reliable basis for studies on 18S rRNA. Sequencing gels on uncloned amplified rDNA confirmed the absence of methylated cytosine in this DNA. The 18S sequence lacks major open reading frames.

We report sequence data from a cloned rDNA unit from Xenopus borealis, extending leftwards from the 18S gene to overlap a region previously sequenced by R.Bach, B.Allet and M.Crippa (Nucleic Acids Research 9,[5311][5312][5313][5314][5315][5316][5317][5318][5319][5320][5321][5322][5323][5324][5325][5326][5327][5328][5329][5330].Comparison with data from other species of Xenopus leads to the inference that the transcription initiation site in X.borealis is in the newly sequenced region and not, as was previously thought, in the region sequenced earlier.The X.borealis external transcribed spacer thus defined is some 612 nucleotides long, about 100 nucleotides shorter than in X.laevis. The X.borealis and X.laevis external transcribed spacers show a pattern of extensive but interrupted sequence divergence, with a large conserved tract starting about 100 nucleotides downstream from the transcription initiation site and shorter conserved tracts elsewhere.The regions in between the conserved tracts differ in length between the respective external transcribed spacers indicating that insertions and deletions have contributed to their divergence, as previously inferred for the internal transcribed spacers.Much of the overall length difference is in the region flanking the 18S gene, where there are also length microheterogeneities in X.laevis rDNA.As in X.laevis, the transcribed spacer sequences flanking the 18S gene in X.borealis contain no major tracts of mutual complementarity. The accumulated data on transcribed spacers in Xenopus render it unlikely that processing of ribosomal precursor RNA involves interaction between the regions flanking 18S RNA.