Different roles of the human Orc6 protein in the replication initiation process

• Published in: Cellular and molecular life sciences : CMLS Vol. 68; no. 22; pp. 3741 - 3756
• Main Authors: Thomae, Andreas W., Baltin, Jens, Pich, Dagmar, Deutsch, Manuel J., Ravasz, Máté, Zeller, Krisztina, Gossen, Manfred, Hammerschmidt, Wolfgang, Schepers, Aloys
• Format: Journal Article
• Language: English
• Published: Basel SP Birkhäuser Verlag Basel 01.11.2011; Springer Nature B.V
• Subjects: Biochemistry; Biomedical and Life Sciences; Biomedicine; Cell Biology; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Chromatin; Deoxyribonucleic acid; DNA; DNA Replication; HEK293 Cells; HMGA1a Protein - chemistry; HMGA1a Protein - genetics; HMGA1a Protein - metabolism; Humans; Life Sciences; Molecular biology; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Origin Recognition Complex - genetics; Origin Recognition Complex - metabolism; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Subunits - genetics; Protein Subunits - metabolism; Proteins; Replication Origin; Research Article; Chromatin; Orc6; HMGA1a; Origin recognition complex; Replication initiation
• ISSN: 1420-682X; 1420-9071
• DOI: 10.1007/s00018-011-0675-9

In eukaryotes, binding of the six-subunit origin recognition complex (ORC) to DNA provides an interactive platform for the sequential assembly of pre-replicative complexes. This process licenses replication origins competent for the subsequent initiation step. Here, we analyze the contribution of human Orc6, the smallest subunit of ORC, to DNA binding and pre-replicative complex formation. We show that Orc6 not only interacts with Orc1–Orc5 but also with the initiation factor Cdc6. Biochemical and imaging experiments reveal that this interaction is required for licensing DNA replication competent. Furthermore, we demonstrate that Orc6 contributes to the interaction of ORC with the chaperone protein HMGA1a (high mobility group protein A1a). Binding of human ORC to replication origins is not specified at the level of DNA sequence and the functional organization of origins is poorly understood. We have identified HMGA1a as one factor that might direct ORC to AT-rich heterochromatic regions. The systematic analysis of the interaction between ORC and HMGA1a revealed that Orc6 interacts with the acidic C-terminus of HMGA1a and also with its AT-hooks. Both domains support autonomous replication if targeted to DNA templates. As such, Orc6 functions at different stages of the replication initiation process. Orc6 can interact with ORC chaperone proteins such as HMGA1a to facilitate chromatin binding of ORC and is also an essential factor for pre-RC formation.