Expression of protein-coding genes embedded in ribosomal DNA.
Ribosomal DNA (rDNA) is a specialised chromosomal location that is dedicated to high-level transcription of ribosomal RNA genes. Interestingly, rDNAs are frequently interrupted by parasitic elements, some of which carry protein genes. These are non-LTR retrotransposons and group II introns that encode reverse transcriptase-like genes, and group I introns and archaeal introns that encode homing endonuclease genes (HEGs). Although rDNA-embedded protein genes are widespread in nuclei, organelles and bacteria, there is surprisingly little information available on how these genes are expressed. Exceptions include a handful of HEGs from group I introns. Recent studies have revealed unusual and essential roles of group I and group I-like ribozymes in the endogenous expression of HEGs. Here we discuss general aspects of rDNA-embedded protein genes and focus on HEG expression from group I introns in the nucleolus.
Johansen
Steinar D
SD
Department of Molecular Biotechnology, Institute of Medical Biology, University of Tromsø, Tromsø, Norway. steinar.johansen@fagmed.uit.no
Haugen
Peik
P
Nielsen
Henrik
H
D000818:Animals; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics*; D005786:Gene Expression Regulation; D007438:Introns / Q000235:genetics; D011506:Proteins / Q000235:genetics*
D004251:DNA Transposable Elements; D004275:DNA, Ribosomal; D011506:Proteins