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Background: Kinesins constitute a superfamily of microtubule motor proteins that are found in eukaryotic organisms. Members of the kinesin superfamily perform many diverse cellular functions such as transport of vesicles and organelles, spindle formation and elongation, chromosome segregation, microtubule dynamics and morphogenesis. Only a few kinesins have been characterized in plants including Arabidopsis thaliana. Because of the diverse cellular functions in which kinesins are involved, the number, types and characteristics of kinesins present in the Arabidopsis genome would provide valuable information for many researchers., Results: Here we have analyzed the recently completed Arabidopsis genome sequence and identified sixty-one kinesin genes in the Arabidopsis genome. Among the five completed eukaryotic genomes the Arabidopsis genome has the highest percentage of kinesin genes. Further analyses of the kinesin gene products have resulted in identification of several interesting domains in Arabidopsis kinesins that provide clues in understanding their functions. A phylogenetic analysis of all Arabidopsis kinesin motor domain sequences with 113 motor domain sequences from other organisms has revealed that Arabidopsis has seven of the nine recognized subfamilies of kinesins whereas some kinesins do not fall into any known family., Conclusion: There are groups of Arabidopsis kinesins that are not present in yeast, Caenorhabditis elegans and Drosophila melanogaster that may, therefore, represent new subfamilies specific to plants. The domains present in different kinesins may provide clues about their functions in cellular processes. The comparative analysis presented here provides a framework for future functional studies with Arabidopsis kinesins.

We cloned and characterized a full-length cDNA that encodes a glutamyl-tRNA synthetase (GluRSAt) from Arabidopsis. The GluRSAt is coded by a single gene. A transcript of about 2.3 kb hybridized with the cDNA. The deduced protein from the cDNA contained 719 amino acids with an estimated molecular mass of 81 kDa. Expression of the GluRSAt in E. coli resulted in a protein of the expected size. Comparison of the amino acid sequence GluRSAt to other glutamyl-tRNA synthetases showed strong sequence similarity to cytoplasmic GluRS proteins.

Cyclins are key regulators of a family of protein kinases called cyclin-dependent kinases (Cdks). Specific cyclins interact with specific Cdks to regulate the different transition points in the cell cycle. Six mitotic-like cyclins have previously been reported in Arabidopsis thaliana. Using polymerase chain reaction amplified cyclin-box sequences as probes, two new cyclin cDNAs are isolated from Arabidopsis. The deduced amino acid sequences of the isolated cDNAs (Arath; CycB1;3 and Arath; CycB1;4) show the highest sequence similarity with mitotic cyclins. Arath; CycB1;3 is most homologous to the plant CycB1 group cyclins and contains a conserved motif that is typical of this group. Arath; CycB1;4, while homologous to Arath; CycB1;2, has some features that make it different from other known mitotic-like cyclins. These data suggest the presence of several distinct cyclins of CycB1 group in Arabidopsis. Analysis of expression of three members of CycB1 group (Arath; CycB1;2, Arath; CycB1;3 and Arath; CycB1;4) in different tissues by reverse transcription-polymerase chain reaction using primers corresponding to unique regions of their cDNAs shows that they are differentially expressed in different tissues.

Cyclins, a large family of proteins, are the regulatory subunits of cyclin-dependent protein kinase that are essential activators of cell cycle progression in eukaryotes. Here we report isolation of a new cyclin cDNA (cyclbAt) from Arabibopsis cDNA libraries using polymerase chain reaction amplified cyclin-box sequences as probes. The deduced amino acid sequence of the isolated cDNA showed the highest sequence similarity with mitotic cyclins. However, the nucleotide and predicted amino acid sequence of cyclbAt is different from five other mitotic-like cyclins that have recently been isolated from the same system, indicating that it is a new mitotic-like cyclin. These results, together with previous reports, suggest that there are at least six different mitotic-like cyclins in Arabidopsis. Expression of cyclbAt in yeast G1 cyclin-minus mutant (DL1) rescued the cyclin-minus phenotype, demonstrating, that plant mitotic-like cyclin can complement cyclin function in yeast. Analysis of expression of cyclbAt in different tissues by reverse transcription-polymerase chain reaction using primers corresponding to a unique region of the cDNA showed that cyclbAt is differentially expressed in different tissues with highest expression in flowers and no detectable expression in leaves.

Degenerate oligonucleotide primers corresponding to two conserved regions in animal cyclins were used to amplify cyclin sequences from Arabidopsis thaliana by polymerase chain reaction (PCR). Screening of a floral meristem cDNA library with two distinct PCR-generated cyclin sequences resulted in the isolation of four different cyclin cDNAs. Southern analysis of genomic DNA and sequence information from the isolated clones suggest that there is a family of cyclins in Arabidopsis.