Open reading frames , subunit

Figure 7.5 Model of ferritin (and erythroid a-aminolaevulinate synthase) translation/ribosome binding regulation by IRP. In (a), with IRP not bound to the IRE (1) binding of the 43S preinitiation complex (consisting of the small ribosomal 40S subunit, GTP and Met-tRNAMet) to the mRNA is assisted by initiation factors associated with this complex, as well as additional eukaryotic initiation factors (elFs) that interact with the mRNA to facilitate 43S association. Subsequently (2), the 43S preinitiation complex moves along the 5 -UTR towards the AUG initiator codon, (3) GTP is hydrolysed, initiation factors are released and assembly of the 80S ribosome occurs. Protein synthesis from the open reading frame (ORF) can now proceed. In (b) With IRP bound to the IRE, access of the 43S preinitiation complex to the mRNA is sterically blocked. From Gray and Hentze, 1994, by permission of Oxford University Press.

The disease is caused by a CAG expansion in the SCA6 gene at chromosome 19pl3, which codes for the aia-voltage-dependent calcium channel subunit (Zhuchenko et al., 1997). Six isoforms of this protein have been described. The CAG repeat is within the open reading frame and is predicted to encode Qn domains in... 

The presence of an open reading frame between vnfD and vnfK led to the identification of an additional small subunit type (8, encoded by vnfG) of the VFe protein it has the hexameric structure 012 2 2 ill). A homologous gene exists between anfD and anfK (13a) and encodes a small subunit of the third nitrogenase (R. Eady and R. Pau, unpublished). 

The mung bean (Vigna radiata, Wilczek) sucrose synthase is a tetramer composed of identical subunits of 95 kDa, and its cDNA contains an open reading frame of 2,415 bp that encodes a polypeptide of 805 amino adds with a calculated molecular mass of 92,087 daltons. The recombinant sucrose synthase expressed... 

The molecular mass of the expressed PA-PLAi was estimated to be 110 kDa by SDS-PAGE, and 97.6 kDa by matrix-associated laser desorption/ionization [48]. A value of 97.6 kDa was also obtained from the deduced amino acid sequence of the open reading frame (ORF) [48]. The enzyme purified from bovine testes had an apparent molecular mass of 440 kDa, as determined by size exclusion chromatography [48], suggesting that PA-PLAi exists as a homotetramer of 98 kDa subunits in solution. The molecular mass of bovine brain PA-PLAi, estimated by the same method, was 200 kDa, suggesting that it exists as a homodimer in the brain [48]. 

Figure 4. Organization of representative type 1, II, and III polyketide synthases. Upper modular arrangement of DEBS 1,2,3 subunits Center orientation and arrangement of open reading frames in actinorhodin gene cluster Lower chalcone synthase subunit. AT, acyltransferase ACP, acyl carrier protein KS, ketosynthase KR, ketoreductase DH, dehydratase ER, enoyl reductase TE, thioesterase TA, tailoring enzyme R/T, regulatory/transport related AR aromatase CY, cyclase.

Type II PKS complexes are comprised at a minimum of four types of subunits encoded by discrete open reading frames acyl carrier protein, ketosynthase a, ketosynthase p (also referred to as chain length factor ), and a malonyl CoA acyltransferase responsible for loading acyl-CoA extender units on to the acyl carrier protein subunit (34 Fig. 4). Additional subunits containing ketoreductase, cyclase, or aromatase activity may also occur in more complex type II synthases. Typically, the four core subunits (acyl carrier protein, ketosynthase a, ketosynthase p, and malonyl-CoA acyltransferase) participate in the iterative series of condensation reactions until a specified polyketide chain length is achieved, then folding and cyclization reactions yielding the final... 

The first step in translation is the assembly of the initiation complex. In bacteria, this is done in a three-step process that involves the initiation factors IF-1, IF-2, and IF-3, the 30S and 50S ribosomal subunits, and the hydrolysis of GTP. As shown in Figure 26.10, the first step is the formation of a preinitiation complex consisting of IF-1, IF-3, and the 30S ribosomal subunit. This preinitiation complex binds with high affinity to a translational start site on the mRNA transcript which is close to the 50 end and includes the first codon of the open-reading frame. This codon is called the initiation codon and it is usually AUG, which specifies the amino-acid methionine in the genetic code (Fig. 26.6). 

---