Ribosomal RNA.rRNA genes

Throughout the 2003 mesocosm study, water (50-500 ml) was collected every third day onto 0.8 gm Supor membrane filters (Pall corp.) and stored at -80°C until analysis. Following enumeration of Phaeocystis sp. single cells and colonies, two samples were chosen for molecular determination of the composition of the Phaeocystis sp. community. Gene sequence analysis of Phaeocystis sp. small subunit ribosomal RNA (rRNA) genes from samples collected from a fertilized enclosure early in the experiment when only single cells were present (5 March 2003 single cells 15 ml"1,... 

It has become increasingly apparent that identification and classification of microorganisms can be enhanced by the vast genetic and structural information available in DNA, RNA, and protein sequences. Criteria based on sequences of ribosomal RNA (rRNA) genes have been used to... 

PCR is being used in phylogenetic and evolutionary studies. PCR amplification and screening of ribosomal RNA (rRNA) genes and mitochondrial DNA have been used to estimate relationships between species and subspecies. Besides studies on the relationships of contemporary species, PCR allows studies on extinct species because it can be performed on material in museum collections. Amplification and sequencing of mitochondrial DNA are also used in evolutionary studies. 

Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of... 

Other specialized RNAs, ribosomal RNA (rRNA), transfer RNAs (tRNAs), and small RNA molecules are not translated into protein but have central roles in gene expression and protein synthesis. 

RNAs have a broader range of functions, and several classes are found in cells. Ribosomal RNAs (rRNAs) are components of ribosomes, the complexes that carry out the synthesis of proteins. Messenger RNAs (mRNAs) are intermediaries, carrying genetic information from one or a few genes to a ribosome, where the corresponding proteins can be synthesized. Transfer RNAs (tRNAs) are adapter molecules that faithfully translate the information in mRNA into a specific sequence of amino acids. In addition to these major classes there is a wide variety of RNAs with special functions, described in depth in Part HL... 

Table 3.2. Divergence (%) in 12 mitochondrial protein-coding genes (nucleotide sequence (above diagonal) and amino acid sequence (below diagonal)) and in nucleotide sequences of the mitochondrial large (rrnL) (above diagonal) and small (rrnS) (below diagonal) ribosomal RNA (rRNA) subunits between the sheep-dog (EgG1) and horse-dog (EgG4) strains of Echinococcus granulosus, E. multilocularis (Em) and Taenia crassiceps (Tc). (After Le ef a/., 2002.)...

Ribosomes, the intracellular particles on which proteins are assembled, are highly complex and dynamic entities. The structural framework of ribosomes is provided by ribosomal RNA (rRNA) molecules with which many proteins are associated (summarized in Capowski and Tracy, 2003). Homologous rRNA genes occur in all prokaryotes and eukaryotes. The mitochondrial and chloroplast rRNA genes in eukaryotes clearly have prokaryote affinities (Pace et ai, 1986). The genomic DNA from which ribosomal genes are transcribed, along with any associated spacers, is collectively termed ribosomal DNA (rDNA). Sequences and other data from rDNA and its products,... 

In prokaryotes, RNA transcribed from protein-coding genes (messenger RNA, mRNA), requires little or no modification prior to translation. In fact, many mRNA molecules begin to be translated even before RNA synthesis has finished. However, ribosomal RNA (rRNA) and transfer RNA (tRNA) are synthesized as precursor molecules that do require post-transcriptional processing (see Topics G9 and G10, respectively). 

Approximately 1000 proteins comprise the mitochondrion the majority are encoded on genes located on nuclear DNA. In fact, as seen in Figure 8-5, the mtDNA encodes only 13 proteins. These mtDNA-encoded proteins are the seven subunits (ND1,2,3,4,4L, 5, and 6) of the NADH-dehydrogenase (RC I) one subunit (cytochrome b) of RC III three subunits (CO I, II, and III) of cytochrome c oxidase (RC IV) and two subunits (A6 and A8) of the ATP synthase (RC V).A11 of these proteins are components of the ETC or the ATP synthase involved in OXPHOS. In addition to these 13 proteincoding genes, the mtDNA encodes 22 mitochondrial transfer ribonucleic acids (tRNAs) and two ribosomal RNA (rRNA) molecules (the large 16S rRNA and the small 12S rRNA). 

Most of the DNA sequences which are transcribed give rise to mRNA, which is subsequently translated into protein. However, the most abundant species of RNA are ribosomal RNA (rRNA) and transfer RNA (tRNA), which do not code for protein but function in the process of translation. They are formed by a high level of transcription of a relatively small number of genes (called rRNA and tRNA genes). In bacteria, transcription of all genes is brought about by the enzyme RNA polymerase. 

---