Diversity of Assimilatory Nitrate Reductase Genes From Plankton and Epiphytes Associated with a Seagrass Bed

Assimilatory nitrate reductase gene fragments were isolated from epiphytes and plankton associated with seagrass blades collected from Tampa Bay, Florida, USA. Nitrate reductase genes from diatoms (NR) and heterotrophic bacteria (nasA) were amplified by polymerase chain reaction (PCR) using two sets of degenerate primers. A total of 129 NR and 75 nasA clones from four clone libraries, two from each of epiphytic and planktonic components, were sequenced and aligned. In addition, genomic DNA sequences for the NR fragment were obtained from Skeletonema costatum and Thalassiosira weissflogii diatom cultures. Rarefaction analysis with an operational taxonomic unit cut-off of 6% indicated that diversity of the NR and nasA clone libraries were similar, and that sequencing of the clone libraries was not yet saturated. Phylogenetic analysis indicated that 121 of the 129 NR clones sequenced were similar to diatom sequences. Of the eight non-diatom sequences, four were most closely related to the sequence of Chlorella vulgaris. Introns were found in 8% of the Tampa Bay NR sequences; introns were also observed in S. costatum, but not T. weissflogii. Introns from within the same clone library exhibited close similarity in nucleotide sequence, position and length; the corresponding exon sequences were unique. Introns from within the same component were similar in position and length, but not in nucleotide sequence. These findings raise questions about the function of introns, and mechanisms or time evolution of intron formation. A large cluster of 14 of the 75 nasA sequences was similar to sequences from Vibrio species; other sequences were closely related to sequences from Alteromonas, alpha-proteobacteria and Marinomonas-like species. Biogeographically consistent patterns were observed for the nasA Tampa Bay sequences compared with sequences from other locations: for example, Tampa Bay sequences were similar to those from the South Atlantic Bight, but not the Barents Sea. The Tampa Bay NR clone libraries contained sequences that exhibited phylogenetic similarity with sequences from coastal New Jersey and Monterey Bay, USA. For both NR and nasA, the sequences formed phylogenetic clusters containing nitrate reductase gene fragments that were common to both plankton and epiphyte components, and sequences that were unique to just one component. The implication that some organisms may be differentially represented in epiphytic versus planktonic components of the community suggests that local environmental conditions may have ramifications for regulation of nitrate assimilation processes, community composition, and ecosystem function.     

Clarithromycin and Amoxicillin Susceptibility of Helicobacter pylori Strains Isolated from Adult Patients with Gastric or Duodenal Ulcer in Italy

Wolbachia endosymbiotic bacteria are widespread in arthropods and are also present in filarial nematodes. Almost all filarial species so far examined have been found to harbor these endosymbionts. The sequences of only three genes have been published for nematode Wolbachia (i.e., the genes coding for the proteins FtsZ and catalase and for 16S rRNA). Here we present the sequences of the genes coding for the Wolbachia surface protein (WSP) from the endosymbionts of eight species of filaria. Complete gene sequences were obtained from the endosymbionts of two different species, Dirofilaria immitis and Brugia malayi. These sequences allowed us to design general primers for amplification of the wsp gene from the Wolbachia of all filarial species examined. For these species, partial WSP sequences (about 600 base pairs) were obtained with these primers. Phylogenetic analysis groups these nematode wsp sequences into a coherent cluster. Within the nematode cluster, wsp-based Wolbachia phylogeny matches a previous phylogeny obtained with ftsZ gene sequences, with a good consistency of the phylogeny of hosts (nematodes) and symbionts (Wolbachia). In addition, different individuals of the same host species (Dirofilaria immitis and Wuchereria bancrofti) show identical wsp gene sequences. Received: 10 January 2000 / Accepted: 22 February 2000     

Conservation of motifs within the unusually variable polypeptide sequences of type I restriction and modification enzymes

Type I restriction enzymes comprise three subunits encoded by genes designated hsdR, hsdM, and hsdS; S confers sequence specificity. Three families of enzymes are known and within families, but not between, hsdM and hsdR are conserved. Consequently, interfamily comparisons of M and R sequences focus on regions of putative functional significance, while both inter- and intrafamily comparisons address the origin, nature and role of diversity of type I restriction systems. We have determined the sequence of the hsdR gene for EcoA, thus making available sequences of all three hsd genes of one representative from each family. The predicted R polypeptide sequences share conserved regions with one superfamily of putative helicases, so-called ‘DEAD box’ proteins; these conserved sequences may be associated with the ATP-dependent translocation of DNA that precedes restriction. We also present hsdM and hsdR sequences for EcoE, a member of the same family as EcoA. The sequences of the M and R genes of EcoA and EcoE are at least as divergent as typical genes from Escherichia coli and Salmonella, perhaps as the result of selection favouring diversity of restriction specificities combined with lateral transfer among different species.     

Studies of He-T DNA sequences in the pericentric regions of Drosophila chromosomes

He-T DNA is a complex set of repeated DNA sequences with sharply defined locations in the polytene chromosomes of Drosophila melanogaster. He-T sequences are found only in the chromocenter and in the terminal (telomere) band on each chromosome arm. Both of these regions appear to be heterochromatic and He-T sequences are never detected in the euchromatic arms of the chromosomes (Young et al. 1983). In the study reported here, in situ hybridization to metaphase chromosomes was used to study the association of He-T DNA with heterochromatic regions that are under-replicated in polytene chromosomes. Although the metaphase Y chromosome appears to be uniformly heterochromatic, He-T DNA hybridization is concentrated in the pericentric region of both normal and deleted Y chromosomes. He-T DNA hybridization is also concentrated in the pericentric regions of the autosomes. Much lower levels of He-T sequences were found in pericentric regions of normal X chromosomes; however compound X chromosomes, constructed by exchanges involving Y chromosomes, had large amounts of He-T DNA, presumably residual Y sequences. The apparent co-localization of He-T sequences with satellite DNAs in pericentric heterochromatin of metaphase chromosomes contrasts with the segregation of satellite DNA to alpha heterochromatin while He-T sequences hybridize to beta heterochromatin in polytene nuclei. This comparison suggests that satellite sequences do not exist as a single block within each chromosome but have interspersed regions of other sequences, including He-T DNA. If this is so, we assume that the satellite DNA blocks must associate during polytenization, leaving the interspersed sequences looped out to form beta heterochromatin. DNA from D. melanogaster has many restriction fragments with homology to He-T sequences. Some of these fragments are found only on the Y. Two of the repeated He-T family restriction fragments are found entirely on the short arm of the Y, predominantly in the pericentric region. Under conditions of moderate stringency, a subset of He-T DNA sequences cross-hybridizes with DNA from D. simulans and D. miranda. In each species, a large fraction of the cross-hybridizing sequences is on the Y chromosome.     

Molecular diversity of bacteria in Yunnan yellow cattle (Bos taurs) from Nujiang region, China

The rumen content of four Yunnan Yellow Cattle (Bos taurs) were collected to determine the bacteria diversity by using 16S rRNA gene sequence analysis. A total of 129 sequences were examined and the sequences were referred as 107 OTU (Operational Taxonomy Unit) according to the similarity level of 97% in gene sequence. Similarity analysis revealed that Yunnan Yellow Cattle had 12 sequences (10 OTU) shared 97% or greater similarity with cultured rumen bacteria Butyrivibrio fibrisolvens, Succiniclasticum ruminis, Ruminococcus bromii, Clostridium proteoclasticum, Ruminococcus flavefaciens, Pseudobutyrivibrio ruminis, Jeotgalicoccus psychrophilus, and Prevotella ruminicola, which accounting for 9.3% of the total clones (9.2% of the total OTU). The further 12 sequences (9 OTU) shared 90–97% similarity with cultured bacteria Clostridium aminobutyricum, butyrate-producing bacterium, Schwartzia succinivorans, Prevotella ruminicola, Eubacterium ruminantium, Ruminococcus albus, and Clostridium termitidis, also accounting for 9.3% of the total sequences (8.3% of the total OTU). The remaining 105 sequences (90 OTU) shared less than 90% similarity with cultured bacteria, accounting for 81.4% of the total sequences (82.5% of the total OTU). According to the phylogenetic analysis, all sequences were phylogenetically placed within phyla of low G+C subdivision (accounting for 72.1 and 72.5% of the total clones and OTU, respectively) and CFB subdivision (Cytophaga-Flexibacter-Bacteroides; accounting for 27.9 and 27.5% of the total clones and OTU, respectively). Among the examined clones, rare bacteria Jeotgalicoccus psychrophilus was detected in the rumen of cattle.     

Characterization and evolution of ovine MHC class II DQB sequence polymorphism

The second exons of OLA-DQB genes from 13 merino sheep were sequenced following amplification by the polymerase chain reaction or isolation from a cDNA library. Ten distinct exon 2 sequences, coding for 10 novel amino acid sequences, were characterized in these sheep. The single-strand conformation polymorphism technique was shown to be capable of discriminating between all sequences. This brings the total number of different OLA-DQB exon 2 sequences (nucleotide and amino acid) which have been characterized to 12, and demonstrates that the OLA-DQB region is highly polymorphic with 29% of nucleotide and 46% of amino acid sites showing variation. Evidence is presented that the OLA-DQB sequences belong to at least two lineages of DQB genes. Some ovine DQB sequences are more like bovine DQB counterparts than other ovine DQB sequences suggesting that the artiodactyl DQB gene and allele lineages predate the separation of the ovine and bovine species 20 million years ago.     

Recombinant Protein Secretion in Pseudozyma flocculosa and Pseudozyma antarctica with a Novel Signal Peptide

Secretion of recombinant proteins aims to reproduce the correct posttranslational modifications of the expressed protein while simplifying its recovery. In this study, secretion signal sequences from an abundantly secreted 34-kDa protein (P34) from Pseudozyma flocculosa were cloned. The efficiency of these sequences in the secretion of recombinant green fluorescent protein (GFP) was investigated in two Pseudozyma species and compared with other secretion signal sequences, from S. cerevisiae and Pseudozyma spp. The results indicate that various secretion signal sequences were functional and that the P34 signal peptide was the most effective secretion signal sequence in both P. flocculosa and P. antarctica. The cells correctly processed the secretion signal sequences, including P34 signal peptide, and mature GFP was recovered from the culture medium. This is the first report of functional secretion signal sequences in P. flocculosa. These sequences can be used to test the secretion of other recombinant proteins and for studying the secretion pathway in P. flocculosa and P. antarctica.     

Characterization and Comparative Analysis of DNA from the Pericentric Heterochromatin of Chromosome 2 of Anopheles atroparvus V. Tiel (Culicidae, Diptera)

The library containing DNA sequences from the diffuse pericentric heterochromatin from the right arm ofAnopheles atroparvus V. Tiel (Culicidae, Diptera) chromosome 2 (2R) was generated by use of chromosome microdissection technique. Southern-blot hybridization of the library fragments with the labeled genomic DNA of A. atroparvus and analysis of their primary structure showed that this heterochromatin region contained repeated DNA sequences differed by their primary structure and the number of copies. These were mostly AT-rich sequences harboring the features characteristic of the S/MAR regions. Based on the clones homology to the sequences from the A. gambiae and Drosophila melanogaster genomes, it was demonstrated that the pericentric heterochromatin from the right arm of A. atroparvus chromosome 2 contained gypsy-like transposable elements, as well as the sequences homologous to the structural genes. In situ hybridization with the chromosomes of A. atroparvus and of the two representatives of the Anopheles maculipennis species complex, A. messeae and A. beklemishevi, showed that pericentric regions of all these chromosomes contained DNA sequences homologous to the sequences from the region-specific library. Cloned fragments of conserved repetitive DNA revealed upon interspecific Southern-blot hybridization of the clones with the labeled genomic DNA of A. messeae can be utilized in further investigations of evolutionary rearrangements of the pericentric heterochromatin within the Anopheles maculipennis species complex.     

Divergent T-cell receptor delta chains from marsupials

Complementary DNAs (cDNAs) encoding T-cell receptor delta (TRD) chains from the northern brown bandicoot, Isoodon macrourus, were identified while sequencing expressed sequence tags (ESTs) from a thymus cDNA library. Surprisingly, the I. macrourus TRD sequences were not orthologous to previously published TRD sequences from another Australian marsupial, the tammar wallaby, Macropus eugenii. Identification of TRD genes in the recently completed whole genome sequence of the South American opossum, Monodelphis domestica, revealed the presence of two highly divergent TRD loci. To determine whether the presence of multiple TRD loci accounts for the lack of orthology between the I. macrourus and M. eugenii cDNAs, additional TRD sequences were obtained from both species of marsupials. The results of this analysis revealed that, unlike eutherian mammals, all three species of marsupials have multiple, highly divergent TRD loci. One group of marsupial TRD sequences was closely related to TR sequences from eutherian mammals. A second group of TRD sequences formed a unique marsupial-specific clade, separate from TR sequences from eutherians. An interesting expression pattern of TRD variable (TRDV) and constant (TRDC) segments was evident in cDNAs from I. macrourus and M. eugenii. TRDV and TRDC sequences that were closely related to TRD genes from eutherian mammals were only found in association with each other in cDNAs from both marsupial species. A similar pattern was seen between TRDV and TRDC sequences that were most closely related to other marsupial TRD genes.     

Informativeness of human (dC-dA)n · (dG-dT)n polymorphisms

Abundant human interspersed repetitive DNA sequences of the form (dC-dA)_n · (dG-dT)_n have been shown to exhibit length polymorphisms. Examination of over 100 human (dC-dA)_n · (dG-dT)_n sequences revealed that the sequences differed from each other both in numbers of repeats and in repeat sequence type. Using a set of precise classification rules, the sequences were divided into three categories: perfect repeat sequences without interruptions in the runs of CA or GT dinucleotides (64% of total), imperfect repeat sequences with one or more interruptions in the run of repeats (25%), and compound repeat sequences with adjacent tandem simple repeats of a different sequence (11%). Informativeness of (dC-dA)_n · (dG-dT)_n markers in the perfect sequence category was found to increase with increasing average numbers of repeats. PIC values ranged from 0 at about 10 or fewer repeats to above 0.8 for sequences with about 24 or more repeats. (dC-dA)_n · (dG-dT)_n polymorphisms in the imperfect sequence category showed lower informativeness than expected on the basis of the total numbers of repeats. The longest run of uninterrupted CA or GT repeats was found to be the best predictor of informativeness of (dC-dA)_n · (dG-dT)_n polymorphisms regardless of the repeat sequence category.     

AT-rich sequences containing Arabidopsis-type telomere sequence and their chromosomal distribution in Pinus densiflora

Japanese red pine Pinus densiflora has 2 n=24 chromosomes and after FISH-detection of Arabidopsis-type (A-type) telomere sequences, many telomere signals were observed on these chromosomes at interstitial and proximal regions in addition to the chromosome ends. These interstitial and proximal signal sites were observed as DAPI-positive bands, suggesting that the interstitial and proximal telomere signal sites are composed of AT-rich highly repetitive sequences. Four DNA clones (PAL810, PAL1114, PAL1539, PAL1742) localized at the interstitial telomere signals were selected from AluI-digested genomic DNA library using colony blot hybridization probed with A-type telomere sequences and characterized using FISH and Southern blot hybridization. The AT-contents of these selected four clones were 60.8–76.3%, and repeat units of the telomere sequence and degenerated telomere sequences were found in their nucleotide sequences. Except for two sites of PAL1114, FISH signals of the four clones co-localized with interstitial and proximal A-type telomere sequence signals. FISH signals a showed similar distribution pattern, but the patterns of signal intensity were different among the four clones. PAL810, PAL1539 and PAL 1742 showed similar FISH signal patterns, and the differences were only with respect to the signal intensity of some signal sites. PAL1114 had unique signals that appeared on chromosomes 7 and 10. Based on results of the Southern blot hybridization these four sequences are not arranged tandemly. Our results suggest that the interstitial A-type telomere sequence signal sites were composed of a mixture of several AT-rich repetitive sequences and that these repetitive sequences contained A-type telomere sequences or degenerated A-type telomere sequence repeats.     

Development and Application of PCR Primers for the Detection of the tfd Genes in Delftia acidovorans P4a Involved in the Degradation of 2,4‐D

Primers specific for the genes tfdD, tfdE and tfdF, derived from conserved amino acid sequence motifs of the corresponding homologous enzymes, and primers specific for the genes tfdA and tfdB as well as tfdC taken from the literature were applied in PCR reactions using the genomic DNA of Delftia acidovorans P4a as the template. PCR products were obtained with all primer pairs that were similar in size to those found with the genomic DNA of strains harbouring plasmid pJP4 as the carrier of tfd genes. The nucleotide sequences and the corresponding amino acid sequences of the PCR products obtained with Strain P4a were compared with the sequence databases. According to BLAST analyses, the partial sequences of tfdA and tfdB exhibited a 94–99% degree of identity with the homologous sequences of the 2,4‐D‐degrading strains Achromobacter xylosoxidans subsp. denitrificans EST4002 (pEST4011), Burkholderia sp. RASC, Variovorax paradoxus TV1 (pTV1) and Burkholderia cepacia 2a (pIJB1), whereas the partial sequences of the tfdC, tfdD, tfdE and tfdF genes revealed a 96–100% degree of identity with the homologous sequences of the chlorobenzene‐utilizing strains Ralstonia eutropha NH9 (pENH91), Pseudomonas chlororaphis RW71 and Pseudomonas sp. P51 (pP51).     

Complementary DNA Cloning and Molecular Evolution of Opine Dehydrogenases in Some Marine Invertebrates

The complete complementary DNA sequences of genes presumably coding for opine dehydrogenases from Arabella iricolor (sandworm), Haliotis discus hannai (abalone), and Patinopecten yessoensis (scallop) were determined, and partial cDNA sequences were derived for Meretrix lusoria (Japanese hard clam) and Spisula sachalinensis (Sakhalin surf clam). The primers ODH-9F and ODH-11R proved useful for amplifying the sequences for opine dehydrogenases from the 4 mollusk species investigated in this study. The sequence of the sandworm was obtained using primers constructed from the amino acid sequence of tauropine dehydrogenase, the main opine dehydrogenase in A. iricolor. The complete cDNA sequence of A. iricolor, H. discus hannai, and P. yessoensis encode 397, 400, and 405 amino acids, respectively. All sequences were aligned and compared with published databank sequences of Loligo opalescens, Loligo vulgaris (squid), Sepia officinalis (cuttlefish), and Pecten maximus (scallop). As expected, a high level of homology was observed for the cDNA from closely related species, such as for cephalopods or scallops, whereas cDNA from the other species showed lower-level homologies. A similar trend was observed when the deduced amino acid sequences were compared. Furthermore, alignment of these sequences revealed some structural motifs that are possibly related to the binding sites of the substrates. The phylogenetic trees derived from the nucleotide and amino acid sequences were consistent with the classification of species resulting from classical taxonomic analyses.     

Identification of <Emphasis Type="Italic">S</Emphasis>-haplotype-specific F-box gene in Japanese plum (<Emphasis Type="Italic">Prunus salicina</Emphasis> Lindl.)

Self-incompatibility has been studied extensively at the molecular level in Solanaceae, Rosaceae and Scrophulariaceae, all of which exhibit gametophytic self-incompatibility controlled by a single polymorphic locus containing at least two linked genes, i.e., the S-RNase gene and the pollen-expressed SFB/SLF (S-haplotype-specific F-box/S-locus F-box) gene. However, the SFB gene in Japanese plum (Prunus salicina Lindl.) has not yet been identified. We determined eight novel sequences homologous to the SFB genes of other Prunus species and named these sequences PsSFB. The gene structure of the SFB genes and the characteristic domains in deduced amino acid sequences were conserved. Three sequences from 410 to 2,800 bp of the intergenic region between the PsSFB sequences and the S-RNase alleles were obtained. The eight identified PsSFB sequences showed S-haplotype-specific polymorphism, with 74–83% amino acid identity. These alleles were exclusively expressed in the pollen. These results suggest that the PsSFB alleles are the pollen S-determinants of GSI in Japanese plum. Nucleotide sequence data reported are available in the NCBI database under the accession numbers DQ849084–DQ849090 and DQ849118.     

Screening and identification of yeast sequences that cause growth inhibition when overexpressed

To isolate genes that negatively regulate cell growth, we constructed a galactose-inducible expression library with partially digested Saccharomyces cerevisiae genomic DNA fragments inserted downstream of the GAL10 promoter. In all, 240 000 yeast transformants were screened for lethality on galactose medium. From 17 such transformants identified, 16 nonoverlapping DNA sequences were obtained. Restriction mapping and determination of DNA sequences adjacent to the GAL10 promoter indicated that the inserts encoded part or all of the URA2, RBP1, TPK3, SAC7, BOI1, and BNI1 genes, and also open reading frames (ORFs) from chromosomes IV, V, IX, XI, and XIII. Some of the identified sequences lacked the amino-terminal sequences of the ORFs, suggesting that truncated forms of the proteins might be necessary for growth inhibition. The sequence of the pGA108 insert was highly homologous to the telomeric X-element and contained an ARS consensus sequence, suggesting a possible growth inhibitory effect of an RNA molecule. Overexpression of the BNI1ΔN and BOI1ΔN genes, which lacked amino-terminal sequences, was associated with phenotypes similar to those of mutants defective in bud formation. Overexpression of the GIN4 and GIN12 sequences induced elongated buds and a G2/M arrest-like phenotype, respectively. The phenotypes induced by the overexpression of our cloned sequences could result from either a dominant-positive or a dominant-negative effect and, unexpectedly, in one case from an effect of an RNA. Received: 3 June 1996 / Accepted: 1 October 1996     

Microbial community structure analysis of produced water from a high-temperature North Sea oil-field

Molecular and culture-based methods were used to investigate the microbial diversity in produced water obtained from the high-temperature Troll oil formation in the North Sea. 16S rRNA gene libraries were generated from total community DNA, using universal archaeal or bacterial oligonucleotide primer sets. Sequence analysis of 88 clones in the bacterial library indicated that they originated from members of Firmicutes (48 sequences), Bacteroidetes (17 sequences), δ-Proteobacteria (15 sequences), Spirochaetes (5 sequences), Thermotogales (2 sequences) and γ-Proteobacteria (1 sequence). Twenty-two sequences in the archaeal library were close relatives to members of the genera Methanococcus (18 sequences), Methanolobus (3 sequences) and Thermococcus (1 sequence). Most of the bacterial sequences shared less than 95% identity with their closest match in GenBank, indicating that the produced water harbours a unique community of novel bacterial species or genera. Members of the thermophilic genera Thermosipho, Thermotoga, Anaerophaga and Thermovirga were isolated. The Troll formations are not injected with sea water. Thus, dramatic changes of the in situ conditions have been avoided, and a common source of continuous contamination from injection water can be excluded. However, the majority of the organisms detected in the gene libraries were most closely related to cultivated organisms with optimum temperatures for growth well below the in situ reservoir temperature (70°C), indicating that produced water from the Troll platform harbours a substantial amount of non-indigenous organisms. This was confirmed by the isolation of a number of mesophilic and moderately thermophilic organisms that were unable to grow at reservoir temperature.     

Nuclear insertions and heteroplasmy of mitochondrial DNA as two sources of intra‐individual genomic variation in grasshoppers

We examined the level of intra‐individual variation in a region of the mitochondrial genome coding for cytochrome oxydase 1 (COI) in two grasshopper species using a clone‐and‐sequence analysis of hundreds of sequences. In both Locusta migratoria and Chortoicetes terminifera, we found that 60–65% of the clones were unique COI‐like sequences. Among these COI‐like sequences, 70–75% diverged by less than 1% from the real mitochondrial haplotypes, and were likely to represent microheteroplasmic molecules. About 20% of the COI‐like sequences diverged by more than 9% from the mitochondrial haplotypes, and generally included stop codons, suggesting that these sequences were nuclear mitochondrial pseudogenes (NUMTs). Only six sequences, diverging by 2–6% from the mitochondrial haplotypes, were identified as potentially misleading in phylogenetic studies. In addition, we found that five sequences from C. terminifera were associated with mobile elements or repetitive DNA families.     

The occurrence of Ds-like sequences in cereal genomes

Summary The occurrence of DNA sequences similar to the Ds-element of sh-m5933 maize (Ds-like sequences) was studied in other representatives of the Gramineae. The approximate number of copies of such sequences found under gentle and stringent conditions of washing was determined by dot-hybridization. It was shown that in the maize genome the number of copies of Ds-like sequences exceeds about ten-fold the content of such sequences found in wheat, rye and barley genomes. Quantitative differences in Ds-like sequences between wheat species with various genomes and ploidies (when estimated per genome) as well as between different H. vulgare varieties was not determined. The various melting points (T_m) of DNA-duplexes formed when the Ds-element is hybridized with wheat, rye and barley DNA respectively do not show significant differences and are essentially lower than the T_m of the Ds-element (by 8°–9°C). Thus, these duplexes have 9–11% of nucleotide substitutions in comparison to Ds sh-m5933. The data obtained permit one to suppose the presence of a series of Ds-like sequences heterogenous for the length and degree of homology to the Ds-element isolated from the shrunken locus (sh-m5933) of maize DNA.