RESUMO
We have identified the seven genes that constitute the A43 mating-type factor of Coprinus cinereus and compare the organisation of A43 with the previously characterised A42 factor. In both, the genes that trigger clamp cell development, the so-called specificity genes, are separated into alpha and beta loci by 7 kb of noncoding sequence and are flanked by homologous genes alpha-fg and beta-fg. The specificity genes are known to encode two classes of dissimilar homeodomain (HD1 and HD2) proteins and have different allelic forms which show little or no cross-hybridisation. By partial sequencing we identified a divergently transcribed HD1 (a1-2) and HD2 (a2-2) gene in the A43 alpha locus. a2-2 failed to elicit clamp cell development in three different hosts, suggesting that it is non-functional. a1-2 elicited clamp cells in an A42 host that has only an HD2 gene (a2-1) in its alpha locus, thus demonstrating that the compatible A alpha mating interaction is between an HD1 and an HD2 protein. The A43 beta locus contains three specificity genes, the divergently transcribed HD1 and HD2 genes b1-2 and b2-2 and a third HD1 gene (d1-1) that was shown by hybridisation and transformation analyses to be functionally equivalent to d1-1 in A42. An untranscribed footprint of a third A42 HD1 gene, c1-1, was detected between the A43 b2-2 and d1-1 genes by Southern hybridisation.
Assuntos
Coprinus/genética , Proteínas Fúngicas/genética , Genes Fúngicos , Genes Fúngicos Tipo Acasalamento , Proteínas de Homeodomínio/genética , Sequência de Aminoácidos , Dados de Sequência Molecular , RNA Fúngico/genética , Transformação GenéticaRESUMO
The A mating type locus of the mushroom Coprinus cinereus regulates essential steps in sexual development. The locus is complex and contains several functionally redundant, multiallelic genes that encode putative transcription factors. Here, we compare four genes from an A locus designated A42. Overall, the DNA sequences are very different (approximately 50% homology), but two classes of genes can be distinguished on the basis of a conserved homeodomain motif in their predicted proteins (HD1 and HD2). Development is postulated to be triggered by an HD1 and an HD2 gene from different A loci. Thus, proteins encoded by genes of the same locus must be distinguished from those encoded by another locus. Individual proteins of both classes recognize each other using the region N-terminal to the homeodomain. These N-terminal specificity regions (COP1 and COP2) are predicted to be helical and are potential dimerization interfaces. The amino acid composition of the C-terminal regions of HD1 proteins suggests a role in activation, and gene truncations indicate that this region is essential for function in vivo. A corresponding C-terminal region in HD2 proteins can be dispensed with in vivo. We will discuss these predicted structural features of the C. cinereus A proteins, their proposed interactions following a compatible cell fusion, and their similarities to the a1 and alpha 2 mating type proteins of the yeast Saccharomyces cerevisiae.
Assuntos
Coprinus/genética , Proteínas Fúngicas/genética , Genes Fúngicos/genética , Genes Fúngicos Tipo Acasalamento , Proteínas de Homeodomínio/genética , Sequência de Aminoácidos , Sequência de Bases , DNA Complementar/genética , Genoma Fúngico , Proteínas de Homeodomínio/classificação , Fator de Acasalamento , Dados de Sequência Molecular , Peptídeos/genética , Estrutura Secundária de Proteína , Reprodução/genética , Análise de Sequência de DNA , Fatores de Transcrição/genética , Transformação GenéticaRESUMO
The A mating type factor of the fungus Coprinus cinereus regulates essential steps in sexual development. Here we describe features of one of the four specificity genes of the A42 factor. By transformation we show that the gene regulates not only sexual development but also asexual sporulation. DNA sequence analysis shows that the gene beta 1-1, encodes a protein with a DNA binding motif and is thus likely to be a transcription factor. The DNA binding domain is an unusual homeodomain with D replacing the normally invariant N in the recognition helix and apparent absence of helix II. The homeodomain is linked to a helical region related to the POUs domain, which is part of a bipartite DNA binding domain of certain animal transcription factors. Like POU factors, the beta 1-1 protein has regions rich in serine, threonine and proline which are possible transactivation domains. Putative dimerization domains and sites for post-translational modification are described.
Assuntos
Coprinus/fisiologia , Peptídeos/fisiologia , Atrativos Sexuais/fisiologia , Sequência de Aminoácidos , Sequência de Bases , Sítios de Ligação , Northern Blotting , Southern Blotting , Mapeamento Cromossômico , DNA Fúngico/genética , Fator de Acasalamento , Dados de Sequência Molecular , Peptídeos/genética , Peptídeos/metabolismo , Plasmídeos , RNA Fúngico/metabolismo , Alinhamento de Sequência , Homologia de Sequência do Ácido Nucleico , Atrativos Sexuais/metabolismo , Esporos Fúngicos , Fatores de Transcrição/genéticaRESUMO
The A mating-type factor is one of two gene complexes that allows mating cells of the mushroom Coprinus cinereus to recognize self from nonself and to regulate a pathway of sexual development that leads to meiosis and sporulation. We have identified seven A genes separated into two subcomplexes corresponding to the classical A alpha and A beta loci. Four genes, one alpha and three beta, all coding for proteins with a homeo domain-related motif, determine A-factor specificity; their allelic forms are so different in sequence that they do not cross-hybridize. It requires only one of these four genes to be heteroallelic in a cell to trigger A-regulated sexual development, and it is the different combinations of their alleles that generate the multiple A factors found in nature. The other three genes cause no change in cell morphology and may regulate the activity of the four specificity genes.
