A two-element Activator/Dissociation (Ac/Ds) gene trap system was successfully established in rice (Oryza sativa ssp. japonica cv. Nipponbare) to generate a collection of stable, unlinked and single-copy Ds transposants. The germinal transposition frequency of Ds was estimated as an average of 51% by analyzing 4413 families. Study of Ds transposition pattern in siblings revealed that 79% had at least two different insertions, suggesting late transposition during rice development. Analysis of 2057 Ds¯anking sequences showed that 88% of them were unique, whereas the rest within T-DNA. The insertions were distributed randomly throughout the genome; however, there was a bias toward chromosomes 4 and 7, which had two times as many insertions as that expected. A hot spot for Ds insertions was identi®ed on chromosome 7 within a 40-kbp region. One-third of Ds¯anking sequences was homologous to either proteins or rice expressed sequence tags (ESTs), con®rming a preference for Ds transposition into coding regions. Analysis of 200 Ds lines on chromosome 1 revealed that 72% insertions were found in genic region. Anchoring of more than 800 insertions to yeast arti®cial chromosome (YAC)-based EST map showed that Ds transposes preferentially into regions rich in expressed sequences. High germinal transposition frequency and independent transpositions among siblings show that the ef®ciency of this system is suitable for large-scale transposon mutagenesis in rice.

30 EST/STS have been mapped on human chromosome 19 using a highly specific hncDNA library as a source of transcribed sequences. In addition more than 50 sites constituting 19 families of closely related sequences containing at least one transcribed member each were mapped across the chromosome. Chromosome-19 specific hncDNA clones were hybridized to chromosome 19 cosmids that were previously assembled into contigs covering about 80% of Chr19. The hybridization results were verified by PCR. Such an approach to EST mapping provides information on possible locations of genes as transcribed units of genome and on location of repeated elements used for the priming the hncDNA synthesis. Mapped hncDNA sequences may serve as good starting points for the systematic sequencing of transcribed genomic regions.