RESUMO
The concept of transcriptional regulation and base promoter structure of genes in eukaryotic organisms rests on two approaches--the experimental (using different methods of directional mutagenesis) and the comparative molecular (comparison of nucleotide sequences in promoter regions of different genes). Investigation of ciliates has led researchers to the conclusion that the protein-coding genes of these organisms lack the classical eukaryotic regulatory elements in the promoter region. This conclusion is based mainly on the usage of the comparative approach, while experimental investigations of such genes are practically absent so far. In the present paper, the comparative molecular analysis of the promoter regions of genes and analysis of the functional role of tubulin, cathepsin and Hsp 70 5'-uncoding areas was performed using new experimental data obtained during investigation of Stylonychia lemnae alpha-tubulin gene. We suggest a new classification of mechanism of transcriptional regulation of protein-coding genes in stichotrichous ciliates.
Assuntos
Cilióforos/genética , Regulação da Expressão Gênica , Proteínas de Protozoários/genética , Tubulina (Proteína)/genética , Regiões 5' não Traduzidas/genética , Animais , Sequência de Bases , Catepsinas/genética , Genes de Protozoários , Proteínas de Choque Térmico HSP72/genética , Dados de Sequência Molecular , Regiões Promotoras Genéticas , Transcrição GênicaRESUMO
The unique structural and functional organization of macronuclear (somatic nucleus) genome of the spirotrichous ciliates, exemplified by Stylonychia lemnae, has been reviewed. Data on the architecture of S. lemnae nuclear apparatus at interphase and during vegetative cell division, conjugation or autogamy are summarized. Special attention being paid to the structural and functional peculiarities of short macronuclear minichromosomes known to contain protein-coding regions, 5'- and 3'-flanking nontranslated regions, and telomeres. A hypothesis, previously put forward, according to which in the spirotrichous ciliates the telomeres themselves may serve as starting points of replication in minichromosomes, has now received its further substantiation. The recent experimental data, which confirm that 5'-nontranscribed DNA leader sequence of alpha1- and alpha2-tubulin-encoding minichromosomes display at least several regulatory elements typical for eukaryote promoter (TATA-box, CAAT-box, transcriptional initiator), are discussed. Up to now, there is no confirmation with regard to a possible existence in the spirotrichous minichromosomes of specific regulatory sequences capable of controlling both replication and transcription processes.