Cloning and Expression
Wooster et al. (1995) identified the BRCA2 gene by positional cloning of a region on chromosome 13q12-q13 implicated in Icelandic families with breast cancer (612555). The candidate disease gene was likely to be located in a 600-kb interval centered around D13S171. Using yeast artificial chromosome and P1 artificial chromosome contigs to identify trapped exons within that region, Wooster et al. (1995) screened human fetal brain, placental, monocyte, and breast cancer cDNA libraries. They identified a cDNA encoding a 2,329-amino acid protein, but suggested that it may not represent the entire gene. Northern blot analysis demonstrated expression in normal breast epithelial cells, placenta, and a breast cancer cell line (MCF7).
Tavtigian et al. (1996) determined the complete coding sequence and exonic structure of BRCA2 and examined its pattern of expression. The composite BRCA2 cDNA sequence assembled consisted of 11,385 bp, but did not include the polyadenylation signal or poly(A) tail. Conceptual translation of the cDNA revealed an ORF beginning at nucleotide 229 and encoding a protein of 3,418 amino acids. There was no signal sequence at the end of terminus, and there were no obvious membrane-spanning regions. The highest levels of expression were observed in breast and thymus, with slightly lower levels in lung, ovary, and spleen. Tavtigian et al. (1996) noted that the BRCA2 protein, like the BRCA1 protein (113705), is highly charged; roughly one-quarter of the residues are acidic or basic.
Connor et al. (1997) described the mouse Brca2 gene. They sequenced cDNA for the entire 3,329-amino acid Brca2 protein and found that, like Brca1, Brca2 is relatively poorly conserved between humans and mice (approximately 60%). Brca2 was transcribed in a diverse range of mouse tissues, especially the testis, ovary, and midgestation embryo. Brca2 was also expressed in the mammary gland and was apparently induced upon pregnancy. The pattern of expression was strikingly similar to that of Brca1.
Warren et al. (2002) cloned and characterized the chicken Brca2 gene. The gene is organized similarly to the human BRCA2 gene, but is more compact. The chicken gene encodes a protein of 3,399 amino acids, which is poorly conserved with mammalian BRCA2 proteins, having only 37% overall amino acid sequence identity with human BRCA2. However, certain domains are much more highly conserved, indicating functional significance. The authors speculated that knowledge of the evolutionarily divergent chicken Brca2 sequence may be useful in distinguishing sequence variants from mutations in the human BRCA2 gene.