Abstract
Inteins are protein sequences that autocatalytically splice themselves out of protein precursors – analogous to introns – and ligate the flanking regions into a functional protein. Inteins are present in all three kingdoms of life, but have a sporadic distribution. They are found predominantly in proteins involved in DNA replication and repair such as helicases. The distribution of inteins suggests an adaptive function. The evolutionary forces which shaped the observed distribution of inteins are generally unknown. Some authors view inteins only as the selfish elements and argue that frequent horizontal transfer is behind inteins sporadic dissemination (Gogarten et al., 2002). On the other hand, the ancient nature of the inteins and the process of gain/loss could lead to the scattered distribution of inteins among species (Pietrokovski, 2001). It is necessary to note that the exclusively selfish nature of inteins is questionable; recent findings support the hypothesis of possible functional roles of inteins in protein regulation (Callahan et al., 2011). Moreover, both hypotheses were built on a limited number of the intein representatives. The amount of genomic data available for bacteria is enormous and in silico analysis for diverse inteins is warranted. We decided to take advantage of these microbial genomic data and performed comprehensive mining for the inteins using a bioinformatic pipeline. Altogether, 1757 species were analysed from 19 major phyla yielding more than 4500 intein-like sequences. The majority of these bacterial inteins were not described previously. Approximately 55% of the inteins were found in polymerases, helicases, or recombinases (Figure 1). Phylogenetic analysis indicated the complex evolutionary dynamics of inteins which includes horizontal transfers, high evolutionary rates coupled with recurrent gains, and losses. The preponderance of inteins in helicases and reductases is being investigated in terms of functional relevance.
This research has been supported by NIH grant GM44844.
References
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