Biomedical subjects

M A Freire-Picos

Publications and source records attributed to M A Freire-Picos.

11 recordsLinked to original sources

PubMed2001

Haem regulation of the mitochondrial import of the Kluyveromyces lactis 5-aminolaevulinate synthase: an organelle approach.

The enzyme 5-aminolaevulinate acid synthase (ALAS) catalyses the first reaction in the haem biosynthetic pathway. In eukaryotes this protein is translated by cytosolic ribosomes and then targeted to the mitochondria. We present evidence that in the yeast Kluyveromyces lactis haem exerts a feedback control upon the import of the ALAS into mitochondria. The ALAS from K. lactis (KlALAS) contains two haem regulatory motifs (HRM) in the mitochondrial targeting signal. Mutagenesis experiments reveal the involvement of these HRM in the response of the KlALAS to haem.

5-Aminolevulinate Synthetase↗

PubMed2001

The KlCYC1 gene, a downstream region for two differentially regulated transcripts.

KlCYC1 encodes for cytochrome c in the yeast Kluyveromyces lactis and is transcribed in two mRNAs with different 3'-processing points. This is an uncommon transcription mechanism in yeast mRNAs. The 3' sequence encompassing the whole region that is needed to produce both mRNAs is analysed. We have determined identical processing points in K.lactis and in Saccharomyces cerevisiae cells transformed with KlCYC1; positions 698 and 1092 (with respect to the TAA) are the major polyadenylation points. This shows that the cis-elements present in the KlCYC1 3'-untranslated region (3'-UTR) direct a processing mechanism that has been conserved in yeast. In K. lactis there is a high predominance of the shorter transcript (1.14 kb) only at the initial logarithmic growth phase. Interestingly, this growth phase-dependent regulation of 3'-UTR processing is lost when the gene is expressed in S. cerevisiae.

3' Untranslated Regions↗

PubMed2000

Heme-mediated transcriptional control in Kluyveromyces lactis.

Heme is of great importance in oxygen-dependent biological functions, since it serves as a prosthetic group for many proteins related to oxygen-binding, oxidative damage prevention and electron transport. It also regulates gene expression through the action of specific transcriptional regulatory factors. In this paper, we present an analysis of heme-dependent transcriptional regulation of several respiration-related genes in an aerobic respiratory yeast, Kluyveromyces lactis. We also report that the KlHEM13 gene, encoding the heme biosynthetic enzyme coproporphyrinogen oxidase, is under heme and oxygen transcriptional regulation, thereby controlling the synthesis of the effector, heme. KlHEM13 is induced during hypoxia, which represents the first report of a transcriptionally regulated gene with this behaviour in K. lactis.

Base Sequence↗

PubMed2000

Transcript analysis of 203 novel genes from Saccharomyces cerevisiae in hap1 and rox1 mutant backgrounds.

Hap1 and Rox1 are transcriptional regulators that bind regulatory sites in the promoters of oxygen-regulated genes in Saccharomyces cerevisiae. Hap1 is a heme-responsive activator of genes induced in aerobic conditions and Rox1 is a repressor of hypoxic genes in aerobic conditions. We have studied transcriptional regulation of a pool of 203 open reading frames (ORFs) from chromosomes IV, VII, and XIV in wild-type, hap1, and rox1 mutant genetic backgrounds in an attempt to extend the family of oxygen and heme regulated genes. Only three ORFs are significantly repressed by Rox1 but they cannot be considered as typical hypoxic genes because they are not overexpressed during hypoxia.

Carbon-Oxygen Lyases↗

PubMed1999

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.

Alcohol Oxidoreductases↗

PubMed1998

Characterization of promoter regions involved in high expression of KlCYC1.

Functional analysis of the KlCYC1 promoter reveals that sequences located upstream to those already published [Freire-Picos, M. A., Rodríguez-Torres, A. M., Ramil, E., Cerdán, M. E., Breuning, K. D., Hollenberg, C. P. & Zitomer, R. S. (1993) Sequence of a cytochrome c from Kluyveromyces lactis and its upstream region, Yeast 9, 201-204] and extending from positions -780 to -371 are important for maintaining high levels of expression, although this region contains both negative and positive elements. A consensus sequence for interaction with KlCpf1p is present at position -492, into the negative site, and specific protein binding to KlCpf1p has been demonstrated. Deletion of the sequences from positions -413 to -338 diminishes KlCYC1 transcription; protein binding to two sequences included in this activator region is detected and several points of evidence indicate that the complex observed is different from the Hap2/3/4/5p complex. Binding of KlCpf1p and the activator complex to the promoter is constitutive in different carbon sources. Although the promoter contains CCAAT boxes, directed mutagenesis has revealed that they are not related to the moderate de-repression observed in glycerol media.

Base Sequence↗

PubMed1998

The HIS4 gene from the yeast Kluyveromyces lactis.

The Kluyveromyces lactis HIS4 gene was cloned by complementation of a Saccharomyces cerevisiae his4 mutant. Sequence analysis revealed a 2388 bp open reading frame encoding a single polypeptide predicted to encompass three distinct enzymatic activities (phosphoribosyl-AMP cyclohydrolase, phosphoribosyl-ATP pyrophosphohydrolase and histidinol dehydrogenase). This structural organization is strikingly similar to that of the His4 proteins from S. cerevisiae and Pichia pastoris. Transcript analysis detected a single mRNA species of 2.5 kb.

Alcohol Oxidoreductases↗

PubMed1996

PICDI, a simple program for codon bias calculation.

PICDI is a very simple program designed to calculate the Intrinsic Codon Deviation Index (ICDI). The program is available in Macintosh as well a PC format. Requirements for correct input of the sequences have been kept to a minimum and the analysis of sequences up to 2000 codons is very quick. The ICDI is very useful for estimation of codon bias of genes from species in which optimal codons are not known. The availability of a computer program for its calculation will increase its usefulness in the fields of Molecular Biology and Biotechnology.

Codon↗

PubMed1995

Regulation of cytochrome c expression in the aerobic respiratory yeast Kluyveromyces lactis.

Transcriptional regulation of the KlCYC1 gene from the aerobic respiratory yeast Kluyveromyces lactis has been studied. The KlCYC1 gene produces two transcripts of different sizes, in contrast with the single transcripts found for CYC1 and CYC7 from Saccharomyces cerevisiae, and for the CYC gene from Schwanniomyces occidentalis. Both KlCYC1 transcripts respond in the same way to the regulatory signals studied here. The transcription of KlCYC1 is regulated by oxygen and this control is mediated by heme. The KlCYC1 gene is also subject to catabolite repression. Heterologous expression in S. cerevisiae mutants reveals that the factors HAP1 and HAP2 take part in the regulatory mechanism.

Base Sequence↗

PubMed1995

Yeast phylogenetic relationships based on cytochrome c sequences.

The availability of the KICYC1 sequence was used to establish homologies with other cytochrome c genes from yeasts and the fungus Neurospora crassa. In terms of nucleotide composition, the cytochrome c gene from Kluyveromyces lactis showed a higher homology with Schwanniomyces occidentalis than with Saccharomyces cerevisiae, and this point is discussed in regard to the differences found in the codon usage of these yeasts. The deduced amino acidic composition of the protein facilitated comparison of its sequence with other cytochrome c protein sequences and new assignments of phylogenetic relationships. In this context Kluyveromyces lactis was most closely related to Candida krusei.

Cytochrome c Group↗

PubMed1994

Codon usage in Kluyveromyces lactis and in yeast cytochrome c-encoding genes.

Codon usage (CU) in Kluyveromyces lactis has been studied. Comparison of CU in highly and lowly expressed genes reveals the existence of 21 optimal codons; 18 of them are also optimal in other yeasts like Saccharomyces cerevisiae or Candida albicans. Codon bias index (CBI) values have been recalculated with reference to the assignment of optimal codons in K. lactis and compared to those previously reported in the literature taking as reference the optimal codons from S. cerevisiae. A new index, the intrinsic codon deviation index (ICDI), is proposed to estimate codon bias of genes from species in which optimal codons are not known; its correlation with other index values, like CBI or effective number of codons (Nc), is high. A comparative analysis of CU in six cytochrome-c-encoding genes (CYC) from five yeasts is also presented and the differences found in the codon bias of these genes are discussed in relation to the metabolic type to which the corresponding yeasts belong. Codon bias in the CYC from K. lactis and S. cerevisiae is correlated to mRNA levels.

Amino Acids↗