Archain

Abstract: We recently reported a novel human gene, ARCN1, whose predicted protein was named archain and was proposed to play a fundamental role in eukaryotic cell biology (Radice et al. 1995). The protein sequence gave highly conserved matches with partial sequences from Drosophila and rice, which showed 88% and 68% identity, respectively. Furthermore, weaker matches with rodent adaptin molecules, which are involved in intracellular vesicle budding and transport (reviewed in Pearse and Robinson 1990), suggested a similar role for archain. We now show that archain sequences are likely to be present in all eukaryotes and present the full-length sequence of rice archain and derive sequences for the nematode and budding yeast proteins from sequence databases. This analysis was contemporaneous with the identification of archain as ~-COP, a component of the COPI coatomer of intracellular vesicles. If archain sequences are well conserved among eukaryotes, it should be possible to detect cognate genomic sequences from a variety of species with the human cDNA probe. Accordingly, when a "zoo blot" was carried out at low stringency, at least one cross-hybridizing band was seen in DNA from monkey, sheep, hamster, rat, and mouse, as well as chicken. Similarly, a probe isolated from the rice archain cDNA C10911 cross-hybridized with other plant DNAs, including Arabidopsis, sorghum, barley, rye, wheat, and oil palm. However, archain DNA sequences are not sufficiently conserved to detect cross-hybridization between animals and plant sequences (data not shown). Since the report of Radice et al. (1995), many new sequences have been deposited in the databases, and a number of these were found to give highly significant matches with human archain (Table 1). Very close or identical matches were seen with translations of partial cDNA sequences from rat (R. norvegicus) and cow (B. taurus), confirming the zoo blot data. However, the most significant (non-human) match was with a cosmid sequence from the nematode worm, C. elegans, which contains the entire nematode archain gene. Highly significant matches were also seen with new partial cDNA sequences from two further plant species, A. thaliana (cress) and S. tuberosum (potato). Of particular biological significance was the match with a sequence on yeast Chromosome (Chr) VI, from which we were able to determine the yeast archain gene and protein sequence. Furthermore, the presence of a partial yeast cDNA sequence (accession no. T36943) in the database which corresponds to this gene demonstrates its expression. Thus, archain is present in lower, as well as higher, eukaryotes and has probably been conserved throughout eukaryotic evolution. In order to evaluate sequence conservation for the full length of the archain protein, we determined predicted protein sequences from three distantly related species. The rice cDNA C10911 was completely sequenced on both strands (accession no. Z67962), and the major open reading frame was determined. This predicts a rice

Abstract: In eukaryotic cells, intracellular transport is mediated by coated vesicular carriers. Coat proteins I (COPI) vesicles are involved in the retrograde transport from Golgi apparatus to the endoplasmic reticulum. The COPI complex is composed of ADP-ribosylation factor 1 and coatomer comprising seven subunits, termed α–ζ. We isolated and characterised a cDNA sequence from rainbow trout homolog to δ-subunit of COPI complex (δ-COP). Trout δ-COP gene encodes a protein of 509 aa including a characteristic Mu homology domain. Searches at the Ensemble Genome browser identified three additional teleostean δ-COP-like sequences from pufferfish, rice fish, and stickleback. Sequence identity of piscine δ-COP protein sequences is greater than 84%. Moreover, a phylogenetic analysis indicates that δ-COP protein sequences are strongly conserved among vertebrate species. δ-COP homologue is ubiquitously expressed in trout tissues. Quantitative Real-Time RT-PCR revealed that δ-COP is differentially expressed in liver and gill tissue of two rainbow trout strains, the freshwater strain STEELHEAD and the brackish water-adapted strain BORN.