THE TOPOGRAPHY OF CHROMOSOMES AND GENES IN THE NUCLEUS

At present several lines of evidence indicate that the nucleus is func tionally compartmentalized into discrete structures with defined prope rties. For instance, it is well established that the molecular machine s involved in replication, transcription, and RNA processing assemble into morphological entities but it remains unclear whether these corre spond to autonomous ''organelles'' or rather represent temporary accum ulations of either active factors recruited onto DNA templates or inac tive factors stored in the vicinity of genes. According to the latter view, the spatial distribution of genes during interphase should play a major role in the subnuclear organization of nonchromatin components such as replication, transcription, and processing factors, and in th is article we discuss current ideas on the functional compartmentaliza tion of chromosomes and genes within the nucleus. (C) 1996 Academic Pr ess, Inc.