Segmented genome: elementary units of genome structure

Numerous observations, measurements and calculations strongly indicate that both eukaryotic and prokaryotic genomes are built as linear arrays of units of rather uniform size, about 400 base pairs. The units are likely to correspond to early individual genes that existed, presumably, in form of DNA circles. Their combinatorial fusion resulted eventually in formation of the early segmented genomes. The segmented structure of the genomes is, apparently, still maintained by some structural selection pressures. Some of the units can be recognized in the sequences by characteristic sequence motifs at the borders of the units. Identification and characterization of the units, their mapping on the genomes should become an important prerequisite of genome comparisons and genome evolution studies.     

Rice genome organization: the centromere and genome interactions

Over the last decade, many varied resources have become available for genome studies in rice. These resources include over 4000 DNA markers, several bacterial artificial chromosome (BAC) libraries, P-1 derived artificial chromosome (PAC) libraries and yeast artificial chromosome (YAC) libraries (genomic DNA clones, filters and end-sequences), retrotransposon tagged lines, and many chemical and irradiated mutant lines. Based on these, high-density genetic maps, cereal comparative maps, YAC and BAC physical maps, and quantitative trait loci (QTL) maps have been constructed, and 93 % of the genome has also been sequenced. These data have revealed key features of the genetic and physical structure of the rice genome and of the evolution of cereal chromosomes. This Botanical Briefing examines aspects of how the rice genome is organized structurally, functionally and evolutionarily. Emphasis is placed on the rice centromere, which is composed of long arrays of centromere-specific repetitive sequences. Differences and similarities amongst various cereal centromeres are detailed. These indicate essential features of centromere function. Another view of various kinds of interactive relationships within and between genomes, which could play crucial roles in genome organization and evolution, is also introduced. Constructed genetic and physical maps indicate duplication of chromosomal segments and spatial association between specific chromosome regions. A genome-wide survey of interactive genetic loci has identified various reproductive barriers that may drive speciation of the rice genome. The significance of these findings in genome organization and evolution is discussed.     

Bottom-up genome assembly using the Bacillus subtilis genome vector

We established a protocol to construct complete recombinant genomes from their small contiguous DNA pieces and obtained the genomes of mouse mitochondrion and rice chloroplast using a B. subtilis genome (BGM) vector. This method allows the design of any recombinant genomes, valuable not only for fundamental research in systems biology and synthetic biology but also for various applications in the life sciences.     

The Mycoplasma genome

A review is presented of the available data on the nature of chromosomal and extrachromosomal DNA of Mollicutes (mycoplasmas)--the smallest and simplest procaryotic organisms.     

The Drosophila genome

The past year has been a spectacular one for Drosophila research. The sequencing and annotation of the Drosophila melanogaster genome has allowed a comprehensive analysis of the first three eukaryotes to be sequenced-yeast, worm and fly-including an analysis of the fly's influences as a model for the study of human disease. This year has also seen the initiation of a full-length cDNA sequencing project and the first analysis of Drosophila development using high-density DNA microarrays containing several thousand Drosophila genes. For the first time homologous recombination has been demonstrated in flies and targeted gene disruptions may not be far off.     

Microbial genome jambalaya

A report on the third American Society of Microbiology (ASM) and The Institute for Genomic Research (TIGR) Microbial Genomes Conference, New Orleans, USA, 29 January to I February 2003.     

Parasite genome initiatives

During 1993-1994, scientists from developing and developed countries planned and initiated a number of parasite genome projects and several consortiums for the mapping and sequencing of these medium-sized genomes were established, often based on already ongoing scientific collaborations. Financial and other support came from WHO/TDR, Wellcome Trust and other funding agencies. Thus, the genomes of Plasmodium falciparum, Schistosoma mansoni, Trypanosoma cruzi, Leishmania major, Trypanosoma brucei, Brugia malayi and other pathogenic nematodes are now under study. From an initial phase of network formation, mapping efforts and resource building (EST, GSS, phage, cosmid, BAC and YAC library constructions), sequencing was initiated in gene discovery projects but soon also on a small chromosome, and now on a fully fledged genome scale. Proteomics, functional analysis, genetic manipulation and microarray analysis are ongoing to different degrees in the respective genome initiatives, and as the funding for the whole genome sequencing becomes secured, most of the participating laboratories, apart from larger sequencing centres, become oriented to post-genomics. Bioinformatics networks are being expanded, including in developing countries, for data mining, annotation and in-depth analysis.