Sequence alignment and evolutionary comparison of the L10 equivalent and L12 equivalent ribosomal proteins from archaebacteria, eubacteria, and eucaryotes

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Abstract
Summary The genes corresponding to the L10 and L12 equivalent ribosomal proteins (L10e and L12e) ofEscherichia coli have been cloned and sequenced from two widely divergent species of archaebacteria,Halobacterium cutirubrum andSulfolobus solfataricus. The deduced amino acid sequences of the L10e and L12e proteins have been compared to each other and to available eubacterial and eucaryotic sequences. We have identified the hyman P0 protein as the eucaryotic L10e. The L10e proteins from the three kingdoms were found to be colinear. The eubacterial L10e protein is much shorter than the archaebacterial-eucaryotic proteins because of two large deletions, one internal and one at the carboxy terminus. The archaebacterial and eucaryotic L12e proteins were also colinear; the eubacterial protein is homologous to the archaebacterial and eucaryotic L12e proteins, but has suffered rearrangement through what appear to be gene fusion events. Intraspecies comparisons between L10e and L12e sequences indicate the archaebacterial and eucaryotic L10e proteins contain a partial copy of the L12e protein fused to their carboxy terminus. In the eubacteria most of this fusion has been removed by the carboxy terminal deletion. Within the L12e-derived region, a 26-amino acid-long internal modular sequence reiterated thrice in the archaebacterial L10e, twice in the eucaryotic L10e, and once in the eubacterial L10e was discovered. This modular sequence also appears to be present as a single copy in all L12e proteins and may play a role in L12e dimerization, L10e–L12e complex formation, and the function of L10e–L12e complex in translation. From these sequence comparisons a model depicting the evolutionary progression of the L10e and L12e genes and proteins from the primordial state to the contemporary archaebacterial, eucaryotic, and eubacterial states is presented.