Eukaryotes split genes

R. Breathnach, P. Chambon (1981) Organization and expression of eukaryotic split genes coding for proteins. Armu. Rev. Biochem., 50 349-383... 

Nearly all of the RNA of the cell is synthesized (transcribed) in the nucleus, according to the instructions encoded in the DNA. Some of the RNA then moves out of the nucleus into the cytoplasm where it functions in protein synthesis and in some other ways. Many eukaryotic genes consist of several sequences that may be separated in the DNA of a chromosome by intervening sequences of hundreds or thousands of base pairs. The long RNA transcripts made from these split genes must be cut and spliced in the nucleus to form the correct messenger RNA molecules which are then sent out to the ribosomes in the cytoplasm. 

Breathnach R., Chambon P. (1981) Organization and expression eukaryotic of split genes for coding proteins. Annu. 

In prokaryotes there is only one copy of DNA per cell, and in nearly all cases there is only a single copy of a gene. Apart from regulatory DNA and signalling sequences, there are very few silent, or non-translated DNA sequences, in prokaryotes. Moreover, each gene is typically collinear with the amino-acid sequence for which it codes. This is in contrast to the organisation of eukaryotic DNA which is structurally and functionally far more complex the structural parts of genes are split by silent DNA and there are multiple copies of the chromosomes. 

Most genes of higher eukaryotes, such as birds and mammals, are split. Lower eukaryotes, such as yeast, have a... 

Each of these sorts of data also supports the deep split within the archaea, into what Woese, Kandler and Wheelis [10] call Euryarchaeota and Crenarchaeota. What the various data sets do not tell us unequivocally is whether, as a monophyletic assemblage, archaea are more recently diverged from eucarya or instead branch with the bacteria. As chapters in this volume reveal, ribosomal protein genes, those for RNA-polymerase subunits and translation elongation factors and some enzymes of metabolism (HMG-CoA reductase, for example [11]) show strong similarity specifically to their eukaryotic homologs, but others exhibit eubacterial affinities, or seem unique. 

Thus, because of the split nature of the eukaryotic genes, the Beadle and Tatum concept of gene-enzyme relation has to be modified, as one gene can create many proteins and could be written in the language of central dogma as... 

A major difference between prokaryotes and eukaryotes is the presence of intervening sequences (introns) between the coding sequences (exons) in eukaryotes. Introns are especially numerous in higher organisms. For example, the gene for the myosin heavy chain present in rat embryonic skeletal muscle encodes a 1939-residue peptide but occupies a length of 22 kb of DNA. The gene is split into 41 exons, whose transcribed RNA must be cut and spliced at 40 places to form the mRNA. By compari-... 

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