The plant Arabidopsis thaliana (Arabidopsis) has become an important model species for the study of many aspects of plant biology. The relatively small size of the nuclear genome and the availability of extensive physical maps of the five chromosomes provide a feasible basis for initiating sequencing of the five chromosomes. The YAC (yeast artificial chromosome)-based physical map of chromosome 4 was used to construct a sequence-ready map of cosmid and BAC (bacterial artificial chromosome) clones covering a 1.9-megabase (Mb) contiguous region, and the sequence of this region is reported here. Analysis of the sequence revealed an average gene density of one gene every 4.8 kilobases (kb), and 54% of the predicted genes had significant similarity to known genes. Other interesting features were found, such as the sequence of a disease-resistance gene locus, the distribution of retroelements, the frequent occurrence of clustered gene families, and the sequence of several classes of genes not previously encountered in plants.

The complete nucleotide sequence of Saccharomyces cerevisiae chromosome X (745 442 bp) reveals a total of 379 open reading frames (ORFs), the coding region covering approximately 75% of the entire sequence. One hundred and eighteen ORFs (31%) correspond to genes previously identified in S. cerevisiae. All other ORFs represent novel putative yeast genes, whose function will have to be determined experimentally. However, 57 of the latter subset (another 15% of the total) encode proteins that show significant analogy to proteins of known function from yeast or other organisms. The remaining ORFs, exhibiting no significant similarity to any known sequence, amount to 54% of the total. General features of chromosome X are also reported, with emphasis on the nucleotide frequency distribution in the environment of the ATG and stop codons, the possible coding capacity of at least some of the small ORFs (<100 codons) and the significance of 46 non‐canonical or unpaired nucleotides in the stems of some of the 24 tRNA genes recognized on this chromosome.

No abstract

SummaryA fragment of the internal transcribed spacer (ITS-l) adjacent to the 5.8S rRNA gene of 20 myrmicine ant species was sequenced. Sequence comparisons were carried out between 11 species of the tribe Leptothoracini, five species of the tribe Tetramoriini, three species of the tribe Solenopsidini and one species of the tribe Myrmicini. Additionally, the formicine ant Camponotus ligniperda (tribe Camponotini) was analyzed as an outgroup species. Among all investigated species, the fragment had a variable length of =230-380 bp with only a few conserved sequence elements. The sequences of this fragment were perfectly identical within four palearctic populations of Leptothorax acervorum indicating that intraspecifie variation is rather low. Within the species of Tetramoriini (including Anergates atratulus) 94 A. atratulus has as yet been uncertain, however, sequence comparison of the ITS-1 fragment leads to the conclusion that A. atratulus rather belongs to the tribe Tetramoriini than to the Solenopsidini.

In the tribe Leptothoracini, the phylogenetic relationship of socially parasitic ants (Doronomyrmex kutteri, D. goesswaldi and Harpagoxenus sublaevis) and their host species Leptothorax acervorum has been controversial. Even more controversial is the relationship between the socially parasitic ant Chalepoxenus muellerianus and its host species Leptothorax unifasciatus, L. nigriceps, L. interruptus and L. recedens. On the basis of morphological, ecological and ethological criteria it has been argued that socially parasitic ants and their respective hosts always evolved from common ancestors, and hence it has been postulated that these species should be included in common taxonomical groups. This would require the division of the tribe Leptothoracini into two subgroups, one comprising the subgenus Leptothorax (s. str.) and the other the subgenus Myrafant, together with their respective parasitic genera. We have used the polymerase chain reaction (PCR) to compare a 360-bp sequence of the mitochondrial cytochrome b gene of 14 species belonging to the tribe Leptothoracini and an outgroup species Tetramorium impurum (Tetramoriini). The results generally agree with the morphological studies which suggest that a common ancestral species differentiated into host and parasite species. This relationship is very obvious within the Leptothorax (s. str.) group but less pronounced in the species belonging to the Myrafant group. Leptothorax (Temnothorax) recedens shows a greater sequence divergence than the outgroup species T. impurum.