共查询到20条相似文献,搜索用时 31 毫秒
1.
D. A. Mullin D. L. Zies A. H. Mullin N. Caballera B. Ely 《Molecular genetics and genomics : MGG》1997,254(4):456-463
IS511 is an endogenous insertion sequence (IS) of the bacterium Caulobactercrescentus strain CB15 and it is the first Caulobacter IS to be characterized at the molecular level. We determined the 1266-bp nucleotide sequence of IS511 and investigated its genetic organization, relationship to other ISs, and transposition properties. IS511 belongs to a distinct branch of the IS3 family that includes ISRI, IS476, and IS1222, based on nucleotide sequence similarity. The nucleotide sequence of IS511 encodes open reading frames (orfs) designated here as orfA and orfB, and their relative organization and amino acid sequences of the predicted protein products are very similar to those of orfAs and orfBs of other IS3 family members. Nuclease S1 protection assays identified an IS511 RNA, and its 5′ end maps approximately 16 nucleotides upstream of orfA and about six nucleotides downstream of a sequence that is similar to the consensus sequence of C. crescentus housekeeping promoters. Evidence is presented that IS511 is capable of precise excision from the chromosome, and transposition from the chromosome to a plasmid. Transpositional insertions of IS511 occurred within sequences with a relatively high G?+?C content, and they were usually, but not always, flanked by a 4-bp direct repeat that matches a sequence at the site of insertion. We also determined the nucleotide sequence flanking the four endogenous IS511 elements that reside in the chromosome of C. crescentus. Our findings demonstrate that IS511 is a transposable IS that belongs to a branch of the IS3 family. 相似文献
2.
An IS element, termed ISCg2, was identified in the chromosome of Corynebacterium glutamicum ATCC 13032. After screening a cosmid library of the C. glutamicum ATCC 13032 genome, six copies of ISCg2 including their flanking regions were sequenced and analyzed. ISCg2 is 1636 bp in length and has 26-bp imperfect inverted repeats flanked by 3-bp direct repeats. By comparisons with other IS
elements, ISCg2 was classified as a member of the IS30 family of insertion sequences. The six copies of ISCg2 were identical at the nucleotide level and were located in intergenic, AT-rich regions of the chromosome. The regions in
which the six copies of ISCg2 were inserted displayed significant similarities. This similarity extends over a region of 65 bp, which was assumed to be
the target region for ISCg2. Interestingly, five of the six copies of ISCg2 were located adjacent to genes that may be involved in aspartate and glutamate metabolism or its regulation. Investigation
of the distribution of ISCg2 showed that the IS element is restricted to certain C. glutamicum strains. Analysis of various integration regions indicates active transposition of ISCg2 in C. glutamicum.
Received: 7 April 1999 / Accepted: 17 June 1999 相似文献
3.
Identification of transposon-like elements in non-coding regions of tomato ACC oxidase genes 总被引:4,自引:0,他引:4
B. Blume C. S. Barry A. J. Hamilton M. Bouzayen D. Grierson 《Molecular & general genetics : MGG》1997,254(3):297-303
1-aminocyclopropane-1-carboxylate (ACC) oxidase, which catalyses the terminal step in ethylene biosynthesis, is encoded by
a small multigene family in tomato that is differentially expressed in response to developmental and environmental cues. In
this study we report the isolation and sequencing of approximately 2 kb of 5′-flanking sequence of three tomato ACC oxidase
genes (LEACO1, LEACO2, LEACO3) and the occurrence of class I and class II mobile element-like insertions in promoter and intron regions of two of them.
The LEACO1 upstream region contains a 420-bp direct repeat which is present in multiple copies in the tomato genome and is very similar
to sequences in the promoters of the tomato E4 and 2A11 genes. The region covering the repeats resembles the remnant of a retrotransposon. Two copies of a small transposable element,
belonging to the Stowaway inverted repeat element family, have been found in the 5′-flanking sequence and the third intron of LEACO3.
Received: 8 August 1996 / Accepted: 4 November 1996 相似文献
4.
In some species of hagfish, the phenomenon of chromosome elimination occurs during embryogenesis. However, only two repetitive
DNA families are known to be represented in chromosomes that are eliminated from somatic cells of the Japanese hagfish Eptatretus okinoseanus. Using molecular analyses, another germ line-restricted, highly repetitive DNA family has been detected in another Japanese
hagfish, Paramyxine atami. The repeat unit of this family, which is 83 bp long, has been designated “EEPa1”, for Eliminated Element of P. atami 1. DNA filter hybridization using EEPa1 as a probe revealed that this family is shared among several species and is conserved
in the germline DNA. Although eliminated, repetitive DNA that is shared interspecifically has not been reported in hagfish
species, cases of chromatin diminution and chromosome elimination processes have been described previously in other organisms.The
patterns and intensities of hybridization signals suggest that members of the repetitive DNA family defined by EEPa1 have
undergone concerted molecular evolution.
Received: 7 January 1997 / Accepted: 13 May 1997 相似文献
5.
IS911 is a bacterial insertion sequence composed of two consecutive overlapping open reading frames (ORFs [orfA and orfB]) encoding the transposase (OrfAB) as well as a regulatory protein (OrfA). These ORFs are bordered by terminal left and right inverted repeats (IRL and IRR, respectively) with several differences in nucleotide sequence. IS911 transposition is asymmetric: each end is cleaved on one strand to generate a free 3′-OH, which is then used as the nucleophile in attacking the opposite insertion sequence (IS) end to generate a free IS circle. This will be inserted into a new target site. We show here that the ends exhibit functional differences which, in vivo, may favor the use of one compared to the other during transposition. Electromobility shift assays showed that a truncated form of the transposase [OrfAB(1-149)] exhibits higher affinity for IRR than for IRL. While there was no detectable difference in IR activities during the early steps of transposition, IRR was more efficient during the final insertion steps. We show here that the differential activities between the two IRs correlate with the different affinities of OrfAB(1-149) for the IRs during assembly of the nucleoprotein complexes leading to transposition. We conclude that the two inverted repeats are not equivalent during IS911 transposition and that this asymmetry may intervene to determine the ordered assembly of the different protein-DNA complexes involved in the reaction. 相似文献
6.
P. A. Bertram-Drogatz S. Rüberg A. Becker A. Pühler 《Molecular & general genetics : MGG》1997,254(5):529-538
The Rhizobium meliloti MucR protein is known to regulate the biosynthesis of the two exopolysaccharides, succinoglycan and galactoglucan. The mucR gene was successfully overexpressed in Escherichia coli BL21 cells by heat shock induction using a two-plasmid system. Cell extracts of the production strain contained about 20%
of a polypeptide of 17 kDa apparent molecular mass, corresponding to the size expected for MucR. As shown by an electrophoretic
mobility shift assay, these extracts were active in the specific retardation of a 219-bp DNA fragment including 134-bp of
the non-coding region upstream of the mucR gene. Primer extension analysis showed that this DNA fragment was located within the transcribed region upstream of the
mucR gene. Competition experiments revealed that a 44-bp sequence present within the 134-bp upstream of the mucR gene contained the MucR binding site. Although binding of MucR to this site exhibited a moderate dissociation constant of
M, the reaction was highly specific since fragments containing binding sites for the homologous Ros protein from Agrobacterium tumefaciens were not able to compete for MucR binding.
Received: 9 October 1996 / Accepted: 20 December 1996 相似文献
7.
Michael J. Webster Timothy P. Scheett Matthew R. Doyle Matthew Branz 《European journal of applied physiology and occupational physiology》1997,75(6):520-524
The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD),
on oxygen uptake (˙VO2), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over
design with a 10-day washout between trials, 14 subjects ingested either 1 g · day−1 of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer
for the determination of ˙VO2submax, ˙VO2peak, lactate concentration ([La− ]), lactate threshold (ThLa) and heart rate ( f
c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with
repeated measures was used to determine significant differences between trials. There were no significant differences detected
between trials for serial measures of ˙VO2submax, [La−] or f
c. Likewise, ˙VO2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min−1, P = 0.83], ThLa [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min−1, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation
does not influence high-intensity exercise performance.
Accepted: 19 December 1996 相似文献
8.
A transposable element, Flipper, was isolated from the phytopathogenic fungus Botrytis cinerea. The element was identified as an insertion sequence within the coding region of the nitrate reductase gene. The Flipper
sequence is 1842 bp long with perfect inverted terminal repeats (ITRs) of 48 bp and an open reading frame (ORF) of 533 amino
acids, potentially encoding for a transposase; the element is flanked by the dinucleotide TA. The encoded protein is very
similar to the putative transposases of three elements from other phytopathogenic fungi, Fot1 from Fusarium oxysporum, and Pot2 and MGR586 from Magnaporthe grisea. The number of Flipper elements in strains of B. cinerea varied from 0 to 20 copies per genome. Analysis of the descendants of one cross showed that the segregation ratio of Flipper
elements was 2:2 and that the copies were not linked.
Received: 4 December 1996 / Accepted: 21 January 1997 相似文献
9.
Molecular evolution and functional relevance of the chalcone synthase genes of pea 总被引:12,自引:0,他引:12
M. Ito Y. Ichinose H. Kato T. Shiraishi T. Yamada 《Molecular & general genetics : MGG》1997,255(1):28-37
We have isolated seven genomic chalcone synthase (CHS) genes and six classes of CHS cDNA from elicitor-treated pea tissues. Comparison of the nucleotide sequences of the coding regions revealed the existence
of eight members of the CHS gene family in pea. These can essentially be divided into three groups (PSCHS1, 2 and 8; PSCHS3, 4 and 5; and PSCHS6 and 7) on the basis of nucleotide and/or amino acid sequence comparisons of the coding regions, introns and promoter regions. We
previously reported that the accumulation of CHS mRNAs is induced by elicitor treatment. Accumulation of CHS mRNA was observed mainly in roots and very little was found in floral organs. To specifically detect expression of each CHS gene in various types of pea cells, S1 nuclease protection assays were performed. Interestingly, the classification of the
eight members of the CHS gene family based on the sequence identity was found to reflect their expression patterns as determined by the S1 nuclease
protection assay. The first group of CHS genes, PSCHS1, 2 and 8, was strongly induced not only by elicitor treatment and UV irradiation but is also constitutively expressed in root and
flower tissues. The second group, PSCHS3, 4 and 5, was also strongly induced by elicitor treatment and UV irradiation but is constitutively expressed only in root. Expression
of the third group, PSCHS6 and 7 was barely detectable in any of the organs tested and was not influenced by environmental stimuli such as elicitor or UV.
Furthermore, sequence analysis of the promoter region of each member of the CHS gene family revealed that putative cis-regulatory elements, such as Box-I, Box-II and G-Box, were conserved only in PSCHS1, 2, 3, 4 and 5. From these results we propose that an ancestral CHS gene might have given rise to defense response-related (UV irradiation- and elicitor-responsive) and -unrelated (unresponsive)
genes at an early stage of evolution, followed by divergence within these subclasses based upon the developmental program
in pea.
Received: 5 November 1996 / Accepted: 6 February 1997 相似文献
10.
C. J. Coates C. L. Turney M. Frommer D. A. O''Brochta P. W. Atkinson 《Molecular & general genetics : MGG》1997,253(6):728-733
Plasmid-based transposition assays were performed in developing embryos of the Australian sheep blowfly Lucilia cuprina and the Queensland fruit fly Bactrocera tryoni, using the mariner transposable element from Drosophila mauritiana. Transposition products were recovered that were identical in structure to those recovered from D. melanogaster. Only sequences delimited by the mariner terminal repeats were transposed and all insertions occurred at TA residues, and duplicated these. These are the hallmarks
of mariner transpositions observed in the chromosomes of D. melanogaster and D. mauritiana, indicating that the plasmid-based assays are accurate indicators of mariner transposition activity. The recovery of precise transposition products from L. cuprina and B. tryoni demonstrates that mariner should be capable of producing germline transformants in these species. The results obtained from these assays suggests that
they will be extremely useful in determining if mariner can transpose in other non-drosophilid insects and for investigating factors that might affect mariner transposition frequency.
Received: 2 May 1996 / Accepted: 24 September 1996 相似文献
11.
12.
B. Jongsareejit R. N. Z. A. Rahman S. Fujiwara T. Imanaka 《Molecular & general genetics : MGG》1997,254(6):635-642
The gltA gene encoding a glutamate synthase (GOGAT) from the hyperthermophilic archaeon Pyrococcus sp. KOD1 was cloned as a 6.6 kb HindIII-BamHI fragment. Sequence analysis indicates that gltA encodes a 481- amino acid protein (53 269 Da). The deduced amino acid sequence of KOD1-GltA includes conserved regions that
are found in the small subunits of bacterial GOGAT: two cysteine clusters, an adenylate-binding consensus sequence and an
FAD-binding consensus sequence. However, no sequences homologous to the large subunit of bacterial GOGAT were found in the
upstream or downstream regions. In order to examine whether GltA alone can act as a functional GOGAT, GltA was overexpressed
in Escherichia coli BL21 (DE3) cells using an expression plasmid. GltA was purified to homogeneity and shown to be functional as a homotetramer
of approximately 205 kDa, which is equivalent to the molecular weight of the native GOGAT from KOD1, thus indicating that
KOD1-GOGAT is the smallest known active GOGAT. GltA is capable of both glutamine-dependent and ammonia-dependent synthesis
of glutamate. Synthesis of glutamate by KOD1-GltA required NADPH, indicating that this enzyme is an NADPH-GOGAT (EC 1.4.1.13).
The optimum pH for both activities was 6.5. However, GltA exhibited different optimum temperatures for activity depending
on the reaction assayed (glutamine-dependent reaction, 80° C; ammonia-dependent reaction, 90° C).
Received: 30 October 1996 / Accepted: 13 January 1997 相似文献
13.
14.
S. Ohshima M. Murata W. Sakamoto Y. Ogura F. Motoyoshi 《Molecular & general genetics : MGG》1997,254(2):186-194
The Arabidopsis gene Terminal Flower 1 (TFL1) controls inflorescence meristem identity. A terminal flower (tfl1) mutant, which develops a terminal flower at the apex of the inflorescence, was induced by transformation with T-DNA. Using
a plant DNA fragment flanking the integrated T-DNA as a probe, a clone was selected from a wild-type genomic library. Comparative
sequence analysis of this clone with an EST clone (129D7T7) suggested the existence of a gene encoding a protein similar to
that encoded by the cen gene which controls inflorescence meristem identity in Antirrhinum. Nucleotide sequences of the region homologous to this putative TFL1 gene were compared between five chemically induced tfl1 mutants and their parental wild-type ecotypes. Every mutant was found to have a nucleotide substitution which could be responsible
for the tfl1 phenotype. This result confirmed that the cloned gene is TFL1 itself. In our tfl1 mutant, no nucleotide substitution was found in the transcribed region of the gene, and the T-DNA-insertion site was located
at 458 bp downstream of the putative polyadenylation signal, suggesting that an element important for expression of the TFL1 gene exists in this area.
Received: 14 November 1996 / Accepted: 29 November 1996 相似文献
15.
Stem respiration of ponderosa pines grown in contrasting climates: implications for global climate change 总被引:7,自引:0,他引:7
We examined the effects of climate and allocation patterns on stem respiration in ponderosa pine (Pinus ponderosa) growing on identical substrate in the cool, moist Sierra Nevada mountains and the warm, dry, Great Basin Desert. These environments
are representative of current climatic conditions and those predicted to accompany a doubling of atmospheric CO2, respectively, throughout the range of many western north American conifers. A previous study found that trees growing in
the desert allocate proportionally more biomass to sapwood and less to leaf area than montane trees. We tested the hypothesis
that respiration rates of sapwood are lower in desert trees than in montane trees due to reduced stem maintenance respiration
(physiological acclimation) or reduced construction cost of stem tissue (structural acclimation). Maintenance respiration
per unit sapwood volume at 15°C did not differ between populations (desert: 6.39 ± 1.14 SE μmol m−3 s−1, montane: 6.54 ± 1.13 SE μmol m−3 s−1, P = 0.71) and declined with increasing stem diameter (P = 0.001). The temperature coefficient of respiration (Q
10) varied seasonally within both environments (P = 0.05). Construction cost of stem sapwood was the same in both environments (desert: 1.46 ± 0.009 SE g glucose g−1 sapwood, montane: 1.48 ± 0.009 SE glucose g−1 sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater
in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees.
Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher
temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that
under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic
rates may be partially offset by increases in maintenance respiration in large trees growing in CO2-enriched atmospheres.
Received: 4 November 1996 / Accepted: 23 January 1997 相似文献
16.
Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause
is positively correlated with latitude (r
2 = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North
America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude,
so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response
curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14
(T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing
latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results
show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing
responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies
on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore
conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying
circadian pacemaker.
Received: 22 July 1996 / Accepted: 30 September 1996 相似文献
17.
Sherri M. Jones Timothy A. Jones Roshni Shukla 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):631-638
Short-latency vestibular-evoked potentials to pulsed linear acceleration were characterized in the quail. Responses occurred
within 8 ms following the onset of stimuli and were composed of a series of positive and negative peaks. The latencies and
amplitudes of the first four peaks were quantitatively characterized. Mean latencies at 1.0 g ms−1 ranged from 1265 ± 208 μs (P1, N = 18) to 4802 ± 441 μs (N4, N = 13). Amplitudes ranged from 3.72 ± 1.51 μV (P1/N1, N = 18) to 1.49 ± 0.77 μV (P3/N3, N = 16). Latency-intensity (LI) slopes ranged from −38.7 ± 7.3 μs dB−1 (P1, N = 18) to −71.6 ± 21.9 μs dB−1 (N3, N = 15) and amplitude-intensity (AI) slopes ranged from 0.20 ± 0.08 μV dB−1 (P1/N1, N = 18) to 0.07 ± 0.04 μV dB−1 (P3/N3, N = 11). The mean response threshold across all animals was −21.83 ± 3.34 dB re: 1.0 g ms−1 (N = 18). Responses remained after cochlear extirpation showing that they could not depend critically on cochlear activity.
Responses were eliminated by destruction of the vestibular end organs, thus showing that responses depended critically and
specifically on the vestibular system. The results demonstrate that the responses are vestibular and the findings provide
a scientific basis for using vestibular responses to evaluate vestibular function through ontogeny and senescence in the quail.
Accepted: 18 January 1997 相似文献
18.
C. Traeholt 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(3):177-184
Five water monitor lizards, Varanus salvator salvator, and four clouded monitor lizards, Varanus bengalensis nebulosus, were caught on Tioman island in Malaysia. A radio-thermistor transmitter was implanted into the buccal cavity of each animal,
and they were released into an enclosure measuring 5.5 × 6.5 metres. The lizards were observed for 9 and 8 days, respectively,
before and after the parietal eye was covered with aluminium foil. With uncovered parietal eye, both species showed a clear
diurnal rhythm, being active only during day time. After covering the parietal eye, the mean locomotor activity of five V. s. salvator decreased from 791 to 107 min · day–1 but remained unchanged around 850 min · day–1 for V. b. nebulosus. The mean duration of locomotor activity decreased in V. s. salvator and V. b. nebulosus after the parietal eye was covered, but V. b. nebulosus maintained its locomotor activity by increasing the number of locomotor bouts. The water monitor spent very little time on
thermoregulation. Its body temperature ranged between 26.3 and 28.4 °C, which decreased after the parietal eye was covered.
The clouded monitor thermoregulated around 28.8–36.0 °C, which remained unchanged after the parietal eye was covered. In both
species, there was a strong correlation between body temperature and ambient temperature. Behavioural abnormalities were recorded
among V. s. salvator with covered parietal eye. They were often observed to be active by night and often slept outside a burrow. The circadian
rhythm of V. b. nebulosus appeared unaffected by shielding of its parietal eye. Captivity combined with shielded parietal eye induced agonistic behaviour
in both species.
Accepted: 11 September 1996 相似文献
19.
A number of DNA damage-inducible genes (DIN) have been identified in Saccharomyces cerevisiae. In the present study we describe isolation of a novel gene, Din7, the expression of which is induced by exposure of cells to UV light, MMS (methyl methanesulfonate) or HU (hydoxyurea). The
DNA sequence of DIN7 was determined. By comparison of the predicted Din7 amino acid sequence with those in databases we found that it belongs
to a family of proteins which includes S. cerevisiae Rad2 and its Schizosaccharomyces pombe and human homologs Rad13 and XPGC; S. cerevisiae Rad27 and its S. pombe homolog Rad2, and S. pombe Exo I. All these proteins are endowed with DNA nuclease activity and are known to play an important function in DNA repair.
The strongest homology to Din7 was found with the Dhs1 protein of S.␣cerevisiae, the function of which is essentially unknown. The expression of the DIN7 gene was studied in detail using a DIN7-lacZ fusion integrated into a chromosome. We show that the expression level of DIN7 rises during meiosis at a time nearly coincident with commitment to recombination. No inducibility of DIN7 was found after treatment with DNA-damaging agents of cells bearing the rad53-21 mutation. Surprisingly, a high basal level of DIN7 expression was found in strains in which the DUN1 gene was inactivated by transposon insertion. We suggest that a form of Dun1 may be a negative regulator of the DIN7 gene expression.
Received: 30 May 1996 / Accepted: 26 September 1996 相似文献
20.
S. Nakamura S. Asakawa N. Ohmido K. Fukui N. Shimizu S. Kawasaki 《Molecular & general genetics : MGG》1997,254(6):611-620
We constructed a rice Bacterial Artificial Chromosome (BAC) library from green leaf protoplasts of the cultivar Shimokita
harboring the rice blast resistance gene Pi-ta. The average insert size of 155 kb and the library size of seven genome equivalents make it one of the most comprehensive
BAC libraries available, and larger than many plant YAC libraries. The library clones were plated on seven high density membranes
of microplate size, enabling efficient colony identification in colony hybridization experiments. Seven percent of clones
carried chloroplast DNA. By probing with markers close to the blast resistance genes Pi-ta
2
(closely linked to Pi-ta) and Pi-b, respectively located in the centromeric region of chromosome 12 and near the telomeric end of chromosome 2, on average 2.2 ± 1.3
and 8.0 ± 2.6 BAC clones/marker were isolated. Differences in chromosomal structures may contribute to this wide variation
in yield. A contig of about 800 kb, consisting of 19 clones, was constructed in the Pi-ta
2
region. This region had a high frequency of repetitive sequences. To circumvent this difficulty, we devised a “two-step walking”
method. The contig spanned a 300 kb region between markers located at 0 cM and 0.3 cM from Pi-ta
2
. The ratio of physical to genetic distances (> 1,000 kb/cM) was more than three times larger than the average of rice (300
kb/cM). The low recombination rate and high frequency of repetitive sequences may also be related to the near centromeric
character of this region. Fluorescent in situ hybridization (FISH) with a BAC clone from the Pi-b region yielded very clear signals on the long arm of chromosome 2, while a clone from the Pi-ta
2
region showed various cross-hybridizing signals near the centromeric regions of all chromosomes.
Received: 14 August 1996 / Accepted: 2 December 1996 相似文献