DNA replication and transcription of adenovirus (Ad) have been studied extensively as a model eukaryotic system. The dissection and reconstitution of the cell-free DNA replication system using the Ad DNA terminal protein complex (Ad DNAprot) have revealed the detailed mechanism of Ad genome replication (1-3). The Ad genome is a linear DNA of '36 kbp that contains 55-kDa terminal proteins covalently attached to its 5' ends. Replication of the Ad DNA-prot initiates by a protein-priming mechanism in which the 5' terminal nucleotide of the nascent DNA, dCMP, is linked to the 80-kDa

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Background: We have studied the nucleosome structure formed from ␣-satellite DNA bound with CENP-B and core histones, in order to develop a previous proposal that the CENP-B dimer may play a critical role in the assembly of higher order structures of the human centromere by juxtaposing CENP-B boxes in long ␣-satellite arrays.

Recent studies have demonstrated that a distinct subpopulation with stem cell-like characteristics in myoblast culture is responsible for new muscle fiber formation after intramuscular transplantation. The identification and isolation of stem-like cells would have significant implications for successful myogenic cell transfer therapy in human muscle disorders. Using a clonal culture system for mouse muscle satellite cells, we have identified two cell types, designated `round cells' and `thick cells', in clones derived from single muscle satellite cells that have been taken from either slow or fast muscle. Clonal analysis of satellite cells revealed that the round cells are immediate descendants of quiescent satellite cells in adult muscle. In single-myofiber culture, round cells first formed colonies and then generated progeny, thick cells, that underwent both myogenic and osteogenic terminal differentiation under the appropriate culture conditions. Thick cells, but not round cells, responded to terminal differentiation-inducing signals. Round cells express Pax7, a specific marker of satellite cells, at high levels. Myogenic cell transfer experiments showed that round cells reconstitute myofibers more efficiently than thick cells. Furthermore, round cells restored dystrophin in myofibers of mdx nude mice, even when as few as 5000 cells were transferred into the gastrocnemius muscle. These results suggest that round cells are satellite-cell descendants with stem cell-like characteristics and represent a useful source of donor cells to improve muscle regeneration.

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