Untranslated Sequence

Post-translational modifications to proteins are biochemical in origin and alter the measured molecular mass relative to that calculated for an untranslated sequence. 

Synthesis of the transferrin receptor (TfR) and that of ferritin are reciprocally linked to cellular iron content. Specific untranslated sequences of the mRNAs for both proteins (named iron response elements) interact with a cytosolic protein sensitive to variations in levels of cellular iron (iron-responsive element-binding protein). When iron levels are high, cells use stored ferritin mRNA to synthesize ferritin, and the TfR mRNA is degraded. In contrast, when iron levels are low, the TfR mRNA is stabilized and increased synthesis of receptors occurs, while ferritin mRNA is apparently stored in an inactive form. This is an important example of control of expression of proteins at the translational level. 

Figure 2. Restriction map of the A. aculeatus rhgA genomic clone plM803. pIM803 contains a 3.9-kb chromosomal Ba/nHI-Sa/1 fragment in pBluescriptSK(-l-). The open reading frame is indicated as closed bars. 5 - and 3 - untranslated sequences and introns are given as open boxes.

Hildinger M., Abel K.L., Ostertag W., and Baum G. (1999) Design of 5 untranslated sequences in retroviral vectors developed for medical use. Journal of Virology 13, 4083 4089. 

In order to optimize expression of proteins in transgenic plants, plant viral untranslated leader sequences are often used (Dowson et al., 1993). Plant viral leaders such as the TMV omega leader sequence can result in an enhancement of expression as great as tenfold. Mitsuhara et al. (1996) compared mRNA and protein levels and determined that mRNA containing the TMV leader sequence was translated more efficiently. This 5 untranslated sequence of TMV is routinely used for high transgene expression (Koziel et al., 1996). 

The cDNAs are about 2 kb in length and contain a single open reading frame encoding 383 amino acids, followed by a 600 bp 3 -untranslated sequence. This 3 -untranslated region contains two functional polyadenylation sequences (AAUAAA), which are both used, as demonstrated by RACE-PCR. 

Table 9.2 Analysis of the 229 desaturase ESTs described in databases. For 221 ESTs the 5 -sequence began in the first exon and allowed to deduce the initiation of transcription 6 ESTs had a complete 3 -untranslated sequence which corresponded to the use of the second poly-A signal (at 2740 bp)... 

Figure 9.10 Promoter prediction for Canton-S and Tai desat2. The untranslated sequences upstream of the ATG of the open reading frame have been analyzed for Canton-S or Tai using McPromoter neural network output. The highest probability for the initiation of transcription for Tai desat2 is located in the region near the 16 nt sequence which is absent in the Canton-S sequence. In Canton-S, the 16 nt deletion lowers the probability of the initiation of transcription after the two putative CAAT and TATA boxes and might be the cause of the lack of transcription of desat2 gene in this strain.

The mineralocorticoid receptor (MR) mediates the sodium-retaining effects of aldosterone in the kidney, salivary glands, sweat glands, and colon. The human MR gene was cloned in 1987 and bears structural and functional kinships to the glucocorticoid receptor (11). It consists of 984 amino acids, spans 60 90 kb on chromosome 4q31.2 (50,51) and contains 10 exons including two exons (la and 1 p) that encode different 5 untranslated sequences whose expression is controlled by two different promoters (52). 

Eukaryotic mRNAs often have long 3 untranslated sequences— sequences that follow the stop codon for the protein they encode. These mRNAs generally conclude with a sequence of up to 200 adenosines, the polyadenylic acid (polyA) sequence at the 3 end. This sequence isn t coded by the DNA template for the gene it is added post-transcriptionally. Not all mRNAs are polyadenylated. For example, histone mRNAs lack polyA tails. Polyadenylation seems to play a role in regulating the stability of mRNAs. An early event in the breakdown of some mRNAs is the removal of their polyA tails. 

The leader is the region between the 5 end of the RNA and the initiation codon. It contains untranslated sequences that are involved in ribosome binding, a step essential for translation of the message into a polypeptide. 

Wilcox AS, Khan AS, Hopkins JA, Sikela JM. Use of 3 untranslated sequences of human cDNAs for rapid chromosome assignment and conversion to STSs implications for an expression map of the genome. Nucleic Acids Res. 1991 19 1837-1843. 

Pace, T., Birago, C., Janse, C. J., Picci, L., and Ponzi, M. (1998). Developmental regulation of a Plasmodium gene involves the generation of stage-specific 5 untranslated sequences. Mol. Biochem. Parasitol. 97,45-53. 

A common feature with all mRNA J transcripts is the 5 untranslated sequences. The regulatory role, if any, of these sequences is unknown, but it has been demonstrated for several protooncogenes that non-coding 5 sequences on the mRNA impair translation (Kozak, 1988). Transcripts A and C have the potential to encode for different forms of NGF precursor due to the pres-... 

H. Kawashima (1999). Human prostate CYP3A5 Identification of a unique 5 -untranslated sequence and characterization of purified recombinant protein. Biochem. Biophys. Res. Commun. 260, 676-681. 

Kaneko, Y. Nonoguchi, K. Fukuyama, H. Takano, S. Higashitsuji, H. Nishiyama, H. Takenawa, J. Nakayama, H. Fujita, J. Presence of alternative 5 untranslated sequences and identification of cells expressing ctk transcripts in the brain and testis. Oncogene, 10, 945-952 (1995)... 

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