Neurospora crassa a mating-type region

Two allelic genes responsible for vegetative incompatibility in the fungus Podospora anserina are not essential for cell viability

Vegetative incompatibility is a lethal reaction that destroys the heterokaryotic cells formed by the fusion of hyphae of non-isogenic strains in many fungi. That incompatibility is genetically determined is well known but the function of the genes triggering this rapid cell death is not. The two allelic incompatibility genes, s and S, of the fungus Podospora anserina were characterized. Both encode 30 kDa polypeptides, which differ by 14 amino acids between the two genes. These two proteins are responsible for the incompatibility reaction that results when cells containing s and S genes fuse. Inactivation of the s or S gene by disruption suppresses incompatibility but does not affect the growth or the sexual cycle of the mutant strains. This suggests that these incompatibility genes have no essential function in the life cycle of the fungus.

Molecular analysis of the Coprinus cinereus mating type A factor demonstrates an unexpectedly complex structure

We report here the molecular cloning of the A43 mating type factor from Coprinus cinereus, a basidiomycetous fungus. Our molecular analyses revealed an unexpected source of variation in the A factor. Though genetic studies have demonstrated that A has two subunits, alpha and beta, we located three nonoverlapping fragments in the A43 region that have A factor function following DNA-mediated transformation. The three fragments demonstrate no similarity to one another as judged by restriction enzyme maps and by hybridization on Southern blots. We conclude that the A43 factor is composed of at least three subunits. When strains carrying different A factors are examined by hybridization to the cloned subunits, extensive polymorphism is seen. Both intensity of hybridization and restriction fragment lengths vary between strains. Some strains fail to show any hybridization to a probe. In contrast, other strains from widely separated geographic locations apparently share very similar subunits. From comparative restriction enzyme mapping of A43 and a mutated A43 factor, we inferred that a 12-kb deletion in the A factor was responsible for the constitutive, dominant phenotype of the mutated A factor. The results of transformation experiments support an activator model for the activity of the A factor in regulating the A pathway.

Cloning the mating types of the heterothallic fungus Podospora anserina: developmental features of haploid transformants carrying both mating types

DNAs that encode the mating-type functions (mat+ and mat-) of the filamentous fungus Podospora anserina were cloned with the use of the mating-type A probe from Neurospora crassa. Cloning the full mat information was ascertained through gene replacement experiments. Molecular and functional analyses of haploid transformants carrying both mating types lead to several striking conclusions. Mat+ mat- strains are dual maters. However, the resident mat information is dominant to the mat information added by transformation with respect to fruiting body development and ascus production. Moreover, when dual mating mat+ mat- strains are crossed to mat+ or mat- testers, there is strong selection, after fertilization, that leads to the loss from the mat+ mat- nucleus of the mat information that matches that of the tester. Finally, the mat locus contains at least two domains, one sufficient for fertilization, the other necessary for sporulation.

Cloning of murine TCF-1, a T cell-specific transcription factor interacting with functional motifs in the CD3-epsilon and T cell receptor alpha enhancers

CD3-epsilon gene expression is confined to the T cell lineage. We have recently identified and cloned a human transcription factor, TCF-1, that binds to a functional element in the T lymphocyte-specific enhancer of CD3-epsilon. In a panel of human cell lines, TCF-1 expression was restricted to T lineage cells. TCF-1 belonged to a novel family of genes that contain the so-called high mobility group 1 (HMG) box. Here we report the cloning of murine TCF-1. Two splice alternatives were identified that were not previously observed in human TCF-1. Murine and human TCF-1 displayed a 95.5% overall amino acid homology. Recombinant murine and human TCF-1 recognized the same sequence motif in the CD3-epsilon enhancer as judged by gel retardation and methylation interference assays. With the murine cDNA clones several aspects of TCF-1 were analyzed. First, deletion analysis revealed that a region of TCF-1 containing the HMG box was sufficient for sequence-specific binding. Second, by high stringency Northern blotting and in situ hybridization, TCF-1 expression was shown to be confined to the thymus and to the T cell areas of the spleen. Third, TCF-1 bound specifically to a functional T cell-specific element in the T cell receptor alpha (TCR-alpha) enhancer. The T lineage-specific expression and the affinity for functional motifs in the TCR-alpha and CD3-epsilon enhancers imply an important role for TCF-1 in the establishment of the mature T cell phenotype.

LEF-1, a gene encoding a lymphoid-specific protein with an HMG domain, regulates T-cell receptor alpha enhancer function [corrected]

Lymphoid-specific cDNA clones were isolated that encode a nuclear protein with homology to the chromosomal nonhistone protein HMG-1 and to putative regulators of cell specialization, including the mammalian testis-determining factor SRY and fungal mating-type proteins. The gene represented by the isolated cDNA clones, termed LEF-1 (lymphoid enhancer-binding factor 1), is developmentally regulated and expressed in pre-B and T lymphocytes but not in later-stage B cells or nonlymphoid tissues. Both endogenous and recombinant LEF-1 were shown to bind to a functionally important site in the T-cell antigen receptor (TCR) alpha enhancer. Maximal TCR alpha enhancer activity was found to parallel the cell type-specific expression pattern of LEF-1. Moreover, forced expression of recombinant LEF-1 in late stage B cells increases TCR alpha enhancer function. Taken together, these data suggest that LEF-1 is a regulatory participant in lymphocyte gene expression and differentiation.

Neurospora crassa A mating-type region

The mating-type locus of the haploid filamentous fungus Neurospora crassa is a regulatory region that controls entry into the sexual cycle and prevents formation of mixed mating-type heterokaryons in the vegetative phase. The locus consists of alternative sequences called A and a. The A mating-type DNA sequence of Neurospora crassa is composed of a region of 5301 base pairs that has little similarity to the sequence present at the mating-type locus in an a mating-type strain. However, the sequences flanking the mating-type locus in the A haploid and a haploid genome are essentially identical. The region of the A mating-type sequence required for expression of the heterokaryon incompatibility and sexual functions has been localized to a single open reading frame (ORF) encoding a polypeptide of 288 amino acids. Sequence analysis of sterile, heterokaryon-compatible mutants reveals frameshift mutations in this same ORF. The putative 288-amino acid product has a region of similarity to the MAT alpha 1 polypeptide of Saccharomyces cerevisiae.