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The taxonomic distribution of kleisin subgroups is uneven

ScpA orthologues (prokaryote kleisins) were detected throughout the bacterial kingdom except for a few subdivisions. In archaebacteria, they are missing in Crenarchaeota and Methanothermobacteria. Among eubacteria, the SMC/kleisin pair is apparently non-orthologously displaced (Galperin and Koonin, 1998; Koonin et al., 1996) by the MukB/E/F system in a subgroup of gamma-proteobacteria (including Enterobacteriaceae, Pasteurellaceae, and Vibrionaceae) and in e-proteobacteria (see Table 1). As far as currently available sequence data suggest, ScpAs and SMCs exist concomitantly in most Bacteria, but never together with MukB, MukE, or MukF. MukB is structurally related to SMC (Melby et al., 1998). It associates with at least two other proteins, MukE and MukF, and is essential for chromosome partitioning in E.coli (Yamazoe et al., 1999). Given the 3D structural similarity between SMC and MukB (Melby et al., 1998), it is possible that a MukB/MukE/MukF complex represents a functional replacement of the SMC/kleisin complex in the gamma-proteobacteria. All three eukaryotic families (kleisin alpha, beta, and gamma) exist in parallel, but some kleisins are missing in certain branches of the phylogenetic tree. For instance, available sequence data indicate that fungal genomes apparently possess no kleisin- members. Furthermore, we were not able to find an obvious Barren orthologue (kleisin-gamma) in nematodes. On the other hand, kleisin eukaryote families are not restricted to one representative per species but may contain multiple, sequentially very similar but distinct sequences. For example, there are apparently several Scc1's in C. elegans and A. thaliana.

Table 1: Taxonomic distribution of the kleisin families (PDF).

Table legend: All kleisins found in the search (except for fragments and for entries with a sequence identity above 98%) were grouped in a taxonomic tree. The number of non-redundant kleisin sequences is reported in the column "entries". The number of species where kleisins were found is listed in the column "species". For each prokaryote genome, not more than one kleisin was retrieved. Among eukaryotes, several kleisins per species do occur. The following two columns indicate whether SMCs or are a MukB orthologue observed within the taxonomic group (dash: absent, check mark: present). The next four columns show whether a member of the four kleisin groups has been found for the given taxon. Model organisms with extensively sequenced genomes that have been used in analysis are listed for convenience.


Galperin, M. Y., and Koonin, E. V. (1998). Sources of systematic error in functional annotation of genomes: domain rearrangement, non-orthologous gene displacement and operon disruption, In Silico Biol 1, 55-67. [PUBMED]

Koonin, E. V., Mushegian, A. R., and Bork, P. (1996). Non-orthologous gene displacement, Trends Genet 12, 334-6.[PUBMED]

Melby, T. E., Ciampaglio, C. N., Briscoe, G., and Erickson, H. P. (1998). The symmetrical structure of structural maintenance of chromosomes (SMC) and MukB proteins: long, antiparallel coiled coils, folded at a flexible hinge, J Cell Biol 142, 1595-604.[PUBMED]

Yamazoe, M., Onogi, T., Sunako, Y., Niki, H., Yamanaka, K., Ichimura, T., and Hiraga, S. (1999). Complex formation of MukB, MukE and MukF proteins involved in chromosome partitioning in Escherichia coli, Embo J 18, 5873-84.[PUBMED]
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