Fluorescence in situ
hybridization to extended DNA fibers (EDFs) from interphase nuclei is
a powerful technique in high-resolution mapping. The fiber FISH
technique is useful for determining the size of target DNA sequences,
the order of genes or clones and their distances in a large
chromosome region. We succeeded in high resolution FISH mapping of
multigene families, repeated DNA sequences, lambda phage clones, and
BACs on EDFs in wheat and rye. The hybridization signals of DNA
sequences in EDFs were traced with length of up to 2.0 Mb on single
DNA fibers. The lower limit of the detection was 1.0 kb.
K. Nagaki, K Kishii, H. Tsujimoto, and T. Sasakuma (Kihara Inst.
Biol.Res., Yokohama City Univ.)
Analysis of Afa-family repetitive sequence from Leymus
racemosus
We isolated Afa-family repetitive sequences from Leymus
racemosus (2n = 4x = 28, Genome NNXX). These sequences repeat
tandem in L. racemosus using 340-bp as one unit. In situ
hybridization using the Afa-family sequence revealed that the
sequences locate on the subtelomeric and interstitial regions of all
L. racemosus chromosomes. This repetitive family occupied
about 1 % of L. racemosus genomes. The restriction sites,
AfaI and AluI, were conserved as seen in the Afa-family
sequences of the other species. Phylogenic analysis indicated that
the Afa-family sequences of L. racemosus clustered near those
of Ht genome of Elymus trachycaulus.
Y. Mukai (Osaka Kyoiku Univ.)
Repetitive DNA sequences present near useful genes in wheat
Agronomically important genes in wheat are mostly isolated from
large-insert genomic DNA libraries such as lambda phage clones,
cosmids, and BACs. These DNA clones usually contain highly repeated
sequences. From distribution patterns on chromosomes by fluorescence
in situ hybridization (FISH), repetitive DNA sequences were
classified into several types: uniformly dispersed type; localized
(dotted) type; telomeric (terminal) type; and centromeric (proximal)
type. These repeated sequences were also visualized on extended DNA
fibers by FISH. Biological function and evolutionary significance of
repeated sequences were discussed.
Y. Matsuoka and K. Tsunewaki (Dept. Biosci., Fukui Pref.
Univ.)
Characterization of
copia-like retrotransposon families in grass
Four grass copia-like retrotransposon families (named G1,
G2, G3, and G4) have been identified by phylogenetic analysis of 177
reverse transcriptase clones obtained from several grass species
including wheat, rice and maize. Elements of G1 and G2 were detected
in various subfamilies of Poaceae by Southern hybridization, whereas
elements of G3 and G4 were restricted to a few given subfamilies.
Comparative analyses of two well sampled families (G1 and G4) showed
that the percentage of elements carrying non-functional reverse
transcriptase domain is high in G4, suggesting that this family may
employ a non-autonomous mechanism for amplification.