de Nobel H, Pike J, Lipke P N, Kurjan J
Department of Microbiology and Molecular Genetics, University of Vermont, College of Medicine 05405-0068, USA.
Mol Gen Genet. 1995 May 20;247(4):409-15. doi: 10.1007/BF00293141.
The Saccharomyces cerevisiae cell adhesion protein a-agglutinin is composed of an anchorage subunit (Aga1p) and an adhesion subunit (Aga2p). Although functional a-agglutinin is expressed only by a cells, previous results indicated that AGA1 RNA is expressed in both a and alpha cells after pheromone induction. Expression of the Aga2p adhesion subunit in alpha cells allowed a-agglutinability, indicating that alpha cells express the a-agglutinin anchorage subunit, although no role for Aga1p in alpha cells has been identified. Most of the a-specific agglutination-defective mutants isolated previously were defective in AGA1; a single mutant (La199) was a candidate for an aga2 mutant. Expression of AGA2 under PGK control allowed secretion of active Aga2p from control strains but did not complement the La199 agglutination defect or allow secretion of Aga2p from La199, suggesting that the La199 mutation might identify a new gene required for a-agglutinin function. However, the La199 agglutination defect showed tight linkage to aga2::URA3 and did not complement aga2::URA3 in a/a diploids. The aga2 gene cloned from La199 was nonfunctional and contained an ochre mutation. The inability of pPGK-AGA2 to express functional Aga2p in La199 was shown to result from an additional mutation(s) that reduces expression of plasmid-borne genes. AGA2 was mapped to the left arm of chromosome VII approximately 28 cM from the centromere.
酿酒酵母细胞黏附蛋白 a-凝集素由一个锚定亚基（Aga1p）和一个黏附亚基（Aga2p）组成。虽然功能性 a-凝集素仅由 a 细胞表达，但先前的结果表明，在信息素诱导后，AGA1 RNA 在 a 细胞和α细胞中均有表达。在α细胞中表达 Aga2p 黏附亚基可使细胞具有 a-凝集性，这表明α细胞表达 a-凝集素锚定亚基，尽管尚未确定 Aga1p 在α细胞中的作用。先前分离出的大多数 a 特异性凝集缺陷突变体在 AGA1 中存在缺陷；一个单一突变体（La199）是 aga2 突变体的候选者。在 PGK 控制下表达 AGA2 可使对照菌株分泌活性 Aga2p，但不能弥补 La199 的凝集缺陷，也不能使 La199 分泌 Aga2p，这表明 La199 突变可能鉴定出一个 a-凝集素功能所需的新基因。然而，La199 的凝集缺陷与 aga2::URA3 紧密连锁，并且在 a/a 二倍体中不能弥补 aga2::URA3。从 La199 克隆的 aga2 基因无功能，且含有一个赭石突变。pPGK-AGA2 在 La199 中无法表达功能性 Aga2p，这被证明是由一个额外的突变导致的，该突变降低了质粒携带基因的表达。AGA2 被定位到染色体 VII 的左臂，距离着丝粒约 28 cM。
