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The structure and organization of a human repetitive DNA family containing the HindIII 1.8-kb repetitive sequence were studied, using two-dimensional (2D) gel electrophoresis. The HindIII 1.8-kb sequence proved to be part of a repetitive sequence about 5 kb long and interspersed on the genome. The long repetitive sequence family contained several subgroups, as based on polymorphism of the restriction site. Recombinant phages containing the long repetitive sequence were isolated from the human genomic DNA library. Heteroduplex and restriction analysis showed that the structure of the repetitive sequence carried by the phages was close to that expected from 2D gel electrophoretic analysis. The 2D gel electrophoretic analysis was shown to be a reliable and useful approach for surveying and mass analysis of repetitive sequence families.

The human prealbumin gene has been cloned and its complete nucleotide sequence determined. The gene has a size of about 6.9 kb and is composed of four exons and three introns. Two Alu family sequences having opposing polarity were found in introns. In the 5'-flanking region, we found two overlapping sequences which have extensive homology to the glucocorticoid-responsive element. Three sequences identical with the enhancer core sequence were identified in introns and the 3' -flanking region. Unusual tandem repeats of a sequence, TTTTG, were also found m the 5'-flanking region and introns.

Sequences homologous to the ribosomal DNA (rDNA) m a Xenopus anucleolate (nucleolus-less) mutant were analyzed by Southern blot analysis. The mutant was found to possess a variety of sequences homologous to non-transcribed spacer (NTS) and/or coding region of rDNA. 65 rDNA-homologous clones were isolated from a genomic DNA library of the mutant. All the clones showed only partial homology to the normal rDNA unit and their restriction maps differed from that of the normal rDNA unit. Based on the hybridization patterns, the rDNA-homologous clones were divided into four groups (I–IV). Structure of group IV, which most strongly hybridized to normal rDNA probe, was analyzed by nucleotide sequencing. The group IV sequence was found to contain a part of the rDNA, including Bam island, enhancer element, promoter region, external transcribed spacer, and a portion of 18 S rRNA gene. The blotting analysis suggested that the group IV sequence is specific for a particular strain of Xenopus.

The nucleotide sequence of the rDNA fragment containing the 3' terminus of the 26S rRNA gene of Physarum polycephalum was determined. By comparing this result with the RNA sequencing data, the 3' terminus of the gene was precisely determined. Possible secondary structures of the region and their implication in transcription termination were discussed.