ISSN:
1550-7408
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
We characterized nine macronuclear tubulin gene minichromosomes in the hypotrich ciliate Euplotidium itoi: two α-tubulin genes, five β-tubulin genes, and two γ-tubulin genes. In particular, one peculiar β-tubulin gene was identified. It shows only 81.5% amino acid similarity to the other characterized β-tubulin types and an UAG stop codon in frame. Based on this result we started to analyse stop codon usage in Euplotidium itoi macronuclear tubulin genes and some unrelated macronuclear minichromosomes. Most of the ciliates independently evolved diverse non-canonical genetic codes. Differences to the standard code consist in the reassignment of one or two of the three standard stop codons to encode a particular amino acid. Class Spirotrichea represents a particular case comprising two groups of organisms that do not share any stop codon. In oxytrichids, UAR is translated as glutamine and UGA is the single stop codon. This is in contrast to the genus Euplotes, close relatives of Euplotidium, in which UAR encodes a stop signal and UGA is translated as cysteine. Fourteen complete genes were characterized in Euplotidium itoi; in all cases UAA revealed as the single triplet used to code a stop, UGA was never and UAG rarely observed in frame. The UAG stop codon was observed in the peculiar type 3 β-tubulin gene, in two dynein partial sequences and in some other putative genes. We could confirm the active expression of three of these genes, the unusual β-tubulin, a putative lipase and a possible steroid-binding protein, by RT-PCR. Finally, a detailed analysis on the structure of the macronuclear tubulin genes, including nucleotide and amino acid differences among tubulin gene paralogs, polyadenylation sites, putative chromosome fragmentation sites, ATGC-content in coding and non-coding regions, telomere sequence and length will be presented.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1550-7408.2005.05202003_6_9.x
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