XMCM7, a novel member of the Xenopus MCM family, interacts with XMCM3 and colocalizes with it throughout replication.

A minichromosome maintenance (MCM) protein complex has been implicated in restricting DNA replication to once per cell cycle in Xenopus egg extracts, based on the behavior of a single protein, XMCM3. Using a two-hybrid screen with XMCM3, we have identified a novel member of the MCM family in Xenopus that is essential for DNA replication. The protein shows strong homology to Saccharomyces cerevisiae MCM7 (CDC47) and has thus been named XMCM7. XMCM7 is present in a multiprotein complex with other MCM proteins. It binds to chromatin and is displaced from chromatin by the act of replication. XMCM7 does not preferentially colocalize with sites of DNA replication but colocalizes with XMCM3 throughout replication. Immunodepletion of the MCM complex from Xenopus egg extract by anti-XMCM7 antibodies inhibits DNA replication of sperm and permeable HeLa G2 nuclei but not permeable HeLa G1 nuclei. Replication capacity of the Xenopus egg extract immunodepleted of the MCM complex by anti-XMCM7 antibody can be rescued by MCM proteins eluted from anti-XMCM3 antibody. We conclude that both proteins are present in the same complex in Xenopus egg extract throughout the cell cycle, that they remain together after binding to chromatin and during DNA replication, and that they perform similar functions.

Functional activation of the human ventrolateral frontal cortex during mnemonic retrieval of verbal information.

Regional cerebral blood flow was measured with positron emission tomography during the performance of a verbal free recall task, a verbal paired associate task, and tasks that required the production of verbal responses either by speaking or writing. Examination of the differences in regional cerebral blood flow between these conditions demonstrated that the left ventrolateral frontal cortical area 45 is involved in the recall of verbal information from long-term memory, in addition to its contribution to speech. The act of writing activated a network of areas involving posterior parietal cortex and sensorimotor areas but not ventrolateral frontal cortex.