Polymerases, eukaryotic

Fig. 26-4A) synthesized DNA normally. This finding stimulated an intensive search for new polymerases. Two were found DNA polymerases II (gene pol B)264 and III. Both are present in amounts less than 25% of that of DNA polymerase I.265 266 Both have properties similar to those of polymerase I, but there are important differences. By now DNA polymerases have been isolated from many organisms, many genes have been cloned and many sequences, both of bacterial and eukaryotic polymerases are known. Comparisons of both sequences and three-dimensional structures,266a/b a few of which are shown in Fig. 27-12, suggest that the polymerases belong to at least six families (Table 27-1). These include the RNA-dependent DNA polymerases known as reverse transcriptases as well as some RNA polymerases.267 2681... 

The 335-residue catalytic subunit of eukaryotic polymerase (3, which has a DNA repair function, is the simplest known DNA polymerase. The active... 

Many of the proteins of eukaryotic replication are closely related in sequences and functions to those of bacteria. There are initiator proteins analogous to E. coli dnaA (Fig. 27-19). The DNA polymerases have been discussed in Section C, 2 (see Table 27-1). Eukaryotic polymerases a and 8 and possibly e are essential for replication.470 471 Polymerase a, which is inhibited specifically by the fungal metabolite aphi-docolin,472 is a complex of a -170-kDa DNA polymerase core, an RNA-synthesizing primase consisting... 

The best characterized family X member is DNA pol [1, the smallest eukaryotic polymerase. Although family X polymerases seem to have evolved separately from other classes of DNA polymerases, they share... 

Eukaryotic polymerase II promoter server Exlnt database ExPASy, tools FlyBase GDB GenBank,... 

These three levels were demonstrated very nicely in the analysis of the primary structure of the large subunits of the RNA polymerases of H. halobium and H. morrhuae (Leffers et al., 1989). Analysis of the gene cluster coding for these subunits identified the amino acid sequences of four polypeptides B", B, A, and C. When these sequences were aligned with the sequences of known RNA polymerases, the B" + B subunits fitted the eukaryotic polymerase IIB subunit of yeast and the (3 subunit of the E. coli polymerase, where they... 

The Transcription Products of All Three Eukaryotic Polymerases Are Processed... 

Eukaryotes have four different RNA polymerases (RNA pol). Three are required for transcription of nuclear genes and the fourth for transcription of mitochondrial genes (Fig. 11.6). RNA polymerase I transcribes ribosomal RNA (rRNA), pol II transcribes mRNA and pol III tRNA and several small RNA s. The three polymerases consist of ten or more subunits. All have two large subunits with homology to the P and p subunits of the prokaryotic RNA polymerase. The three eukaryotic polymerases can be distinguished based on their sensitivity to a-amanitin, a toxin found in some types of mushrooms. RNA pol II activity is severely inhibited, pol III weakly and pol I is insensitive. The antibiotic rifampicin inhibits prokaryotic RNA polymerases. 

Eukaryote polymerase is larger, with more subunits. 

Figure 29.13). The binding site is 12 A from the active site itself. Rifampicin does not hinder chain elongation once initiated, because the RNA-1 )NA hybrid present in the enzyme prevents the antibiotic from binding. The pocket in which rifampicin binds is conserved among bacterial RNA polymerases, but not eukaryotic polymerases, and so rifampicin can be used as an antibiotic in antituberculosis therapy. 

Chary, P. and Lloyd, R.S. (1995) In vitro replication by prokaryotic and eukaryotic polymerases on DNA templates containing site-spedfic and stereospedfic benzo[a]pyrene-7,8-dihy-drodiol-9,10-epoxide adduds. Nucleic Acids Res., 23, 1398-1405. 

Three Eukaryotic Polymerases Catalyze Formation of Different RNAs... 

Figure 11-6). Each of the eukaryotic polymerases also contains an (O-lIke and two nonIdentIcal ct-llke subunits. The extensive similarity In the structures of these core subunits In RNA polymerases from various sources Indicates that this enzyme arose early In evolution and was largely conserved. This seems logical for an enzyme catalyzing a process so basic as copying RNA from DNA. 

In addition to their core subunits related to the E. coli RNA polymerase subunits, all three yeast RNA polymerases contain four additional small subunits, common to them but not to the bacterial RNA polymerase. Finally, each eukaryotic polymerase has several enzyme-specific subunits that are not present In the other two polymerases. Gene-knockout experiments In yeast Indicate that most of these subunits are essential for cell viability. Disruption of the few polymerase subunit genes that are not absolutely essential for viability nevertheless results in very poorly growing cells. Thus It... 

The discovery of the first DNA polymerase, E. coli DNA polymerase I, by Kornberg and co-workers occurred over 50 years ago. After extensive research spanning multiple decades, there are currently seven families of polymerases (A, B, C, D, X, Y, and RT) which are classified according to primary sequence homology and structural similarity. Eukaryotic polymerases belong to four of these families (A, B, X, and Y) (reviewed in Shcherbakova et Hubscher et al., Pavlov et al. and McCulloch and Kunkel ). Defects in proper regulation... 

Notable members comprising the Family B polymerases include the prototypical E. coli Pol II, as well as eukaryotic polymerases, Pol a, Pol S, Pol e, and Pol (. In humans, the coordinated efforts of Pol a, Pol 8, and Pol e are responsible for leading and lagging strand synthesis during nuclear chromosomal replication prior to... 

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