Resumo
A replicação do DNA requer precisão e especificidade. Para garantir este controle, a célula utiliza dois elementos genéticos: uma sequência de nucleotídeos, na qual a duplicação do DNA inicia-se, e uma molécula, ou um complexo proteico, capaz de reconhecer esta região do DNA como uma origem de replicação. Em leveduras e em metazoários, a origem de replicação é reconhecida por um complexo de pré-replicação composto por um heterohexâmero ORC, formado por seis proteínas Orc1-Orc6. O complexo ORC recruta as moléculas Cdc6 e Cdt1, que juntas recrutam o complexo MCM, composto por seis subunidades, que apresenta atividade de helicase e é fundamental para replicação do DNA. Em Archaea, a origem de replicação é reconhecida por apenas uma proteína homóloga tanto a Orc1 quanto a Cdc6, Orc1/Cdc6, que recruta o complexo MCM. Na maioria dos representantes de Archaea, o complexo MCM apresenta-se como um homohexâmero, formado apenas por uma subunidade de MCM. Em Trypanosoma cruzi, o complexo de pré-replicação também é composto por uma molécula Orc1/Cdc6. Em seu genoma, no entanto, encontram-se as seis subunidades de MCM. Estes dados demonstram que T. cruzi apresenta uma maquinaria de pré-replicação mais complexa que a de Archaea, porém mais simples que a dos demais eucariontes.
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Copyright (c) 2010 Patrícia Diogo de Melo GODOY, Simone Guedes CALDERANO, Maria Carolina ELIAS