The skeletal function of non-genic nuclear DNA: new evidence from ancient cell chimaeras.

摘要: DNA can be divided functionally into three categories: (1) genes — which code for proteins or specify non-messenger RNAs; (2) semons short specific sequences involved in the replication, segregation, recombination attachments of chromosomes, chromosome regions (e.g. loops domains) selfish genetic elements; (3) secondary does not function by means sequences. Probably more than 90% biosphere is present nuclei plants and phytoplankton. The amount genic related to complexity organism, whereas increases proportionally with cell volume, complexity. This correlation most simply explained skeletal hypothesis, according nuclear functions as basic framework assembly nucleus total genomic content (together relatively invariant folding rules) determining volumes. Balanced growth during cycle requires cytonuclear ratio basically constant, irrespective volume; thus volumes, therefore overall genome size, have evolutionarily adjusted changing volumes optimal function. Bacteria, mitochondria, chloroplasts viruses no envelope; hypothesis explains why essentially absent from them but large nuclei. Hitherto it has been difficult refute alternative that (whether ‘junk’ DNA) accumulates merely mutation pressure, selection economy strong enough eliminate it, accumulation mitochondria plastids prevented intracellular replicative competition between their multiple genomes. New data discriminate clearly these explanations come cryptomonads chlorarachneans, two groups algae originated independently symbiogenesis (i.e., merger radically different eukaryote cells) several hundred million years ago. In both plasma membrane former algal symbiont persist nucleomorphs periplastid membrane, respectively. fact undergone a 200- 1000-fold reduction size virtually shows against non-functional very efficiently; therefore, amounts host chimaeras, generally, must being maintained positive selection. divergent readily explicable given spectrum gene encodes.