Analysis of the ribosomal protein gene cluster between these 7 organisms shows the expected differences when comparing gene order, gene length, protein similarity, and evolutionary relationships. The intergenic region differences between Mg and Mp and all of the other organisms suggests that this change occurred after the point at which the common ancestor of Uu, and Mg / Mp diverged. The fluctuation in Ig region sizes suggests that these sequences are evolutionarily fluid, and strict conservation is not necessary. Regulatory sequences for protein expression, such as ribosome binding sites must, of course, be conserved, and other regulatory sequences may also be present, but Ig region lengths are never-the-less able to fluctuate within a relatively wide margin. The simplistic explanation that Mg has compressed its Ig region lengths to minimize genome size does not hold up since Mp, with a genome size greater than that of Uu (816 vs. 760 Kbp), also maintains small Ig region lengths similar to Mg. The immediate explanation for the similarity of Ig region lengths between Mg and Mp lies in their close evolutionary relationship. Any further functional explanations such as altered protein expression regulatory mechanisms need additional study. As our annotation of Uu progresses, we hope to extend these observations to other regions of the genome. As sequences from additional organisms become available, they will also be included in these studies. Finally, as sequence similarities and differences within these regions that might provide the genotypic explanation for different regulatory mechanisms become apparent, laboratory studies can be designed to test various predictions that have been derived from these computer-based analyses.
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