RESUMEN
Animal replication-dependent histone genes produce histone proteins for the packaging of newly replicated genomic DNA. The expression of these histone genes occurs during S phase and is linked to DNA replication via S-phase checkpoints. The histone RNA-binding protein HBP/SLBP (hairpin-binding protein/stem-loop binding protein), an essential regulator of histone gene expression, binds to the conserved hairpin structure located in the 3'UTR (untranslated region) of histone mRNA and participates in histone pre-mRNA processing, translation and histone mRNA degradation. Here, we report the accumulation of alternatively spliced HBP/SLBP transcripts lacking exons 2 and/or 3 in HeLa cells exposed to replication stress. We also detected a shorter HBP/SLBP protein isoform under these conditions that can be accounted for by alternative splicing of HBP/SLBP mRNA. HBP/SLBP mRNA alternative splicing returned to low levels again upon removal of replication stress and was abrogated by caffeine, suggesting the involvement of checkpoint kinases. Analysis of HBP/SLBP cellular localization using GFP (green fluorescent protein) fusion proteins revealed that HBP/SLBP protein and isoforms lacking the domains encoded by exon 2 and exons 2 and 3 were found in the nucleus and cytoplasm, whereas HBP/SLBP lacking the domain encoded by exon 3 was predominantly localised to the nucleus. This isoform lacks the conserved region important for protein-protein interaction with the CTIF [CBP80/20 (cap-binding protein 80/20)]-dependent initiation translation factor and the eIF4E (eukaryotic initiation factor 4E)-dependent translation factor SLIP1/MIF4GD (SLBP-interacting protein 1/MIF4G domain). Consistent with this, we have previously demonstrated that this region is required for the function of HBP/SLBP in cap-dependent translation. In conclusion, alternative splicing allows the synthesis of HBP/SLBP isoforms with different properties that may be important for regulating HBP/SLBP functions during replication stress.
Asunto(s)
Empalme Alternativo , Replicación del ADN , Histonas/metabolismo , Proteínas Nucleares/metabolismo , ARN Mensajero/metabolismo , Factores de Escisión y Poliadenilación de ARNm/metabolismo , Secuencia de Aminoácidos , Cafeína/farmacología , Secuencia Conservada , Regulación de la Expresión Génica , Células HeLa , Histonas/genética , Humanos , Datos de Secuencia Molecular , Proteínas Nucleares/genética , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Transporte de Proteínas , ARN Mensajero/genética , Estrés Fisiológico , Factores de Escisión y Poliadenilación de ARNm/genéticaRESUMEN
Histone proteins are essential for the packaging of DNA into chromosomes. Histone gene expression is cell-cycle-regulated and coupled to DNA replication. Control of histone gene expression occurs at the transcriptional and post-transcriptional level and ensures that a fine balance between histone abundance and DNA replication is maintained for the correct packaging of newly replicated DNA into chromosomes. In the present paper, we review histone gene expression, highlighting the control mechanisms and key molecules involved in this process.
Asunto(s)
Expresión Génica/genética , Histonas/metabolismo , Animales , Replicación del ADN/genética , Histonas/genética , Humanos , Procesamiento Postranscripcional del ARN/genética , Procesamiento Postranscripcional del ARN/fisiología , Estabilidad del ARN/genéticaRESUMEN
Candida albicans is a common commensal and opportunistic pathogenic fungus. Although it normally reproduces clonally, several lines of evidence exist for genetic recombination and some form of sexual reproduction. We have sequenced seven regions of its mitochondrial genome in 36 strains and constructed haplotypes for the 66 polymorphic sites, which include single-nucleotide polymorphisms and insertion/deletions. Nineteen different haplotypes were observed. Strains with the same mitochondrial haplotype were found in different clades defined by nuclear multilocus sequence typing (MLST) and the UPGMA dendrograms constructed using either set of data were different in topology. There was no apparent correlation between mitochondrial haplotype and the source of the strain (geographical or anatomical). Examination of the mitochondrial haplotypes revealed substantial evidence for recombination between polymorphic sites. This suggests that the use of mitochondrial haplotypes in phylogenetic studies should be approached with caution. These results provide further evidence for recombination and genetic exchange in the biology of C. albicans.