The HIS4 gene from the yeast Kluyveromyces lactis

Characterization of a gene similar to BIK1 in the yeast Kluyveromyces lactis

In Saccharomyces cerevisiae, Bik1p is a microtubule plus-end-tracking protein that plays several roles in mitosis and ploidy. KlBik1p (from Kluyveromyces lactis) maintains the same structural-domain organization as does S. cerevisiae Bik1p. As part of its characterization, we constructed a stable klbik1 mutant which is sensitive to benomyl only at 14 degrees C and has a higher frequency of crescent-shaped nuclei than S. cerevisiae bik1 mutants. This phenotype is partially rescued by S. cerevisiae BIK1. Other phenotypes associated with bik1 are not present in the K. lactis mutant. By fusion to GFP we were able to show the functionality of the KlBik1p CAP-Gly domain and found that the fusion protein changes its cellular location during the cell cycle.

An expression cDNA library for suppression cloning in yeast mutants, complementation of a yeast his4 mutant, and EST analysis from the symbiotic basidiomycete Hebeloma cylindrosporum

An oriented expression library was constructed from the mycelia of the symbiotic model fungus Hebeloma cylindrosporum in the high-level yeast expression vector pDR196. DNA sequencing of approximately 500 expressed sequence tags (ESTs) showed that 15% correspond to known genes, two thirds contain sequences with unknown function, andthe remaining 20% showed no significant similarity to any known genes. The ESTs had a GC content between 44 and 56%, with most of them having a GC content of 52-54%, which could be correlated with GC contents of fungal genes. The library was successfully used to identify the Hebeloma HIS4 gene by functional complementation of a yeast his4 mutant. Thus, the library may serve as a powerful tool for identification and characterization of mycorrhizal genes by EST analysis and for the identification of ectomycorrhizal genes by means of suppression cloning.

Kluyveromyces lactis HIS4 transcriptional regulation: similarities and differences to Saccharomyces cerevisiae HIS4 gene

Sequence analysis of the Kluyveromyces lactis HIS4 (KlHIS4) gene promoter reveals relevant differences in comparison to the Saccharomyces cerevisiae HIS4 homologous gene. Among them are the absence of a Rap1 binding site and the presence of only three putative Gcn4 binding consensus sites instead of the five described in the S. cerevisiae promoter. Since these factors are implicated in the general control, we investigated the transcriptional regulation of the KlHIS4 gene under conditions of amino acid starvation and discovered that the mechanisms previously described for S. cerevisiae HIS4 regulation and related to general control are not functional in K. lactis. The expression analysis of the KlHIS4 gene under phosphate starvation or high adenine supply shows that factors, such as Bas1 or Bas2, involved in the basal control may also operate in a different way in K. lactis. Interestingly, and also in contrast to the HIS4 regulation in S. cerevisiae, we found domains for Nit2-like and yeast-Ap1-like binding sequences. Northern analyses showed transcriptional activation under ammonia starvation and oxidative stress.

Characterization of the histidine mutants of Kluyveromyces lactis

Thirty-eight different histidine mutations of Kluyveromyces lactis were isolated and genetically characterized. All of the mutations were nuclear recessive alleles. They turned out to belong to seven different complementation groups, designated hisA1 to hisA7. Five of these genes have been cloned by in vivo complementation of the Klhis mutations. Their homology to some of the histidine genes of Saccharomyces cerevisiae was confirmed by heterologous complementation. However, one of these KlHIS genes did not complement any mutation in the seven known histidine biosynthetic enzymes encoding genes (his1-his7) of S. cerevisiae.