Limits...
Regulation of ribosomal RNA gene copy number and its role in modulating genome integrity and evolutionary adaptability in yeast.

Kobayashi T - Cell. Mol. Life Sci. (2011)

Bottom Line: The unusual nature of rRNA gene repeats affects cellular functions such as senescence.In addition, we recently found that the repeat number determines sensitivity to DNA damage.In this review, I would like to introduce a new aspect of the rRNA gene repeat (called rDNA) as a center of maintenance of genome integrity and discuss its contribution to evolution.

View Article: PubMed Central - PubMed

Affiliation: Division of Cytogenetics, National Institute of Genetics/The Graduate University for Advanced Studies, SOKENDAI, 1111 Yata, Mishima, Shizuoka, Japan. takobaya@lab.nig.ac.jp

ABSTRACT
The genes encoding ribosomal RNA (rRNA) are the most abundant genes in the eukaryotic genome. They reside in tandem repetitive clusters, in some cases totaling hundreds of copies. Due to their repetitive structure and highly active transcription, the rRNA gene repeats are some of the most fragile sites in the chromosome. A unique gene amplification system compensates for loss of copies, thus maintaining copy number, albeit with some fluctuations. The unusual nature of rRNA gene repeats affects cellular functions such as senescence. In addition, we recently found that the repeat number determines sensitivity to DNA damage. In this review, I would like to introduce a new aspect of the rRNA gene repeat (called rDNA) as a center of maintenance of genome integrity and discuss its contribution to evolution.

Show MeSH

Related in: MedlinePlus

Structure of the budding yeast rDNA locus. The rDNA is a tandem repeating array on chromosome XII. A repeating unit (9.1 kb) has 5S and 35S rRNA genes and two intergenic spacer regions (IGS1, 2). rARS and RFB are the replication origin and replication fork barrier site, respectively. EXP (~500 bp) is an expansion sequence that contains RFB and E-pro. E-pro is a bidirectional promoter for non-coding transcripts that function in the regulation of rDNA repeat numbers. The rDNA structure is broadly conserved from yeast to human, though in the human genome the 5S rDNA is found in independent arrays
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3064901&req=5

Fig1: Structure of the budding yeast rDNA locus. The rDNA is a tandem repeating array on chromosome XII. A repeating unit (9.1 kb) has 5S and 35S rRNA genes and two intergenic spacer regions (IGS1, 2). rARS and RFB are the replication origin and replication fork barrier site, respectively. EXP (~500 bp) is an expansion sequence that contains RFB and E-pro. E-pro is a bidirectional promoter for non-coding transcripts that function in the regulation of rDNA repeat numbers. The rDNA structure is broadly conserved from yeast to human, though in the human genome the 5S rDNA is found in independent arrays

Mentions: In the budding yeast Saccharomyces cerevisiae, rRNA is transcribed as 35S rRNA and then processed into three mature rRNAs (18S, 5.8S, and 26S, Fig. 1). Together with a small, 5S rRNA, which is transcribed independently from 35S rRNA, these RNA molecules form the skeletal framework of the ribosome [2]. Ribosome is a protein–RNA complex that translates mRNA to protein and it is abundant in the cell. Ribosomal proteins (RP) account for approximately 50% of the total protein and rRNA represents approximately 80% of the total RNA in a yeast cell [3]. To meet this huge biosynthetic demand, eukaryotic cells contain hundreds of copies of rRNA genes organized into clusters. In human cells, there are five rDNA clusters, located in chromosomes 13, 14, 15, 21 and 22. Each cluster contains ~70 copies, bringing the total number of rDNA gene copies to ~350 (~15 Mbp) per haploid genome [4]. In general, plants have more rDNA copies. For example, a pea (Pisum sativum) has ~4,000 copies [5]. In S. cerevisiae, there is a single cluster, comprising approximately 150 copies of rDNA, located on chromosome XII. This cluster covers about 60% of chromosome XII and about 10% of the whole genome [6]. For these reasons, we can reasonably consider the rDNA as the “king of the housekeeping genes” in terms of function and quantity (Fig. 1).Fig. 1


Regulation of ribosomal RNA gene copy number and its role in modulating genome integrity and evolutionary adaptability in yeast.

Kobayashi T - Cell. Mol. Life Sci. (2011)

Structure of the budding yeast rDNA locus. The rDNA is a tandem repeating array on chromosome XII. A repeating unit (9.1 kb) has 5S and 35S rRNA genes and two intergenic spacer regions (IGS1, 2). rARS and RFB are the replication origin and replication fork barrier site, respectively. EXP (~500 bp) is an expansion sequence that contains RFB and E-pro. E-pro is a bidirectional promoter for non-coding transcripts that function in the regulation of rDNA repeat numbers. The rDNA structure is broadly conserved from yeast to human, though in the human genome the 5S rDNA is found in independent arrays
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3064901&req=5

Fig1: Structure of the budding yeast rDNA locus. The rDNA is a tandem repeating array on chromosome XII. A repeating unit (9.1 kb) has 5S and 35S rRNA genes and two intergenic spacer regions (IGS1, 2). rARS and RFB are the replication origin and replication fork barrier site, respectively. EXP (~500 bp) is an expansion sequence that contains RFB and E-pro. E-pro is a bidirectional promoter for non-coding transcripts that function in the regulation of rDNA repeat numbers. The rDNA structure is broadly conserved from yeast to human, though in the human genome the 5S rDNA is found in independent arrays
Mentions: In the budding yeast Saccharomyces cerevisiae, rRNA is transcribed as 35S rRNA and then processed into three mature rRNAs (18S, 5.8S, and 26S, Fig. 1). Together with a small, 5S rRNA, which is transcribed independently from 35S rRNA, these RNA molecules form the skeletal framework of the ribosome [2]. Ribosome is a protein–RNA complex that translates mRNA to protein and it is abundant in the cell. Ribosomal proteins (RP) account for approximately 50% of the total protein and rRNA represents approximately 80% of the total RNA in a yeast cell [3]. To meet this huge biosynthetic demand, eukaryotic cells contain hundreds of copies of rRNA genes organized into clusters. In human cells, there are five rDNA clusters, located in chromosomes 13, 14, 15, 21 and 22. Each cluster contains ~70 copies, bringing the total number of rDNA gene copies to ~350 (~15 Mbp) per haploid genome [4]. In general, plants have more rDNA copies. For example, a pea (Pisum sativum) has ~4,000 copies [5]. In S. cerevisiae, there is a single cluster, comprising approximately 150 copies of rDNA, located on chromosome XII. This cluster covers about 60% of chromosome XII and about 10% of the whole genome [6]. For these reasons, we can reasonably consider the rDNA as the “king of the housekeeping genes” in terms of function and quantity (Fig. 1).Fig. 1

Bottom Line: The unusual nature of rRNA gene repeats affects cellular functions such as senescence.In addition, we recently found that the repeat number determines sensitivity to DNA damage.In this review, I would like to introduce a new aspect of the rRNA gene repeat (called rDNA) as a center of maintenance of genome integrity and discuss its contribution to evolution.

View Article: PubMed Central - PubMed

Affiliation: Division of Cytogenetics, National Institute of Genetics/The Graduate University for Advanced Studies, SOKENDAI, 1111 Yata, Mishima, Shizuoka, Japan. takobaya@lab.nig.ac.jp

ABSTRACT
The genes encoding ribosomal RNA (rRNA) are the most abundant genes in the eukaryotic genome. They reside in tandem repetitive clusters, in some cases totaling hundreds of copies. Due to their repetitive structure and highly active transcription, the rRNA gene repeats are some of the most fragile sites in the chromosome. A unique gene amplification system compensates for loss of copies, thus maintaining copy number, albeit with some fluctuations. The unusual nature of rRNA gene repeats affects cellular functions such as senescence. In addition, we recently found that the repeat number determines sensitivity to DNA damage. In this review, I would like to introduce a new aspect of the rRNA gene repeat (called rDNA) as a center of maintenance of genome integrity and discuss its contribution to evolution.

Show MeSH
Related in: MedlinePlus