MRNA function

Although FdUrd produces only DNA-medicated cyotoxicity, 5-FU can also be metabolized to fluorouracil monophosphate (FUMP) and ultimately to fluorouracil triphosphate (FUTP), which can be incorporated into RNA in place of uridine triphosphate (UTP). In other words, incorporation of 5-FU into RNA mimics uracil de novo synthesis and affects the production of ribosomal RNAs (rRNAs) (16,17). 5 -FU also affects several aspects of messenger RNA (mRNA) function, including transcription (18), translation (19), and slicing (20). 

Prokaryotic mRNA is generally identical to its primary transcript, whereas eukaryotic mRNA is extensively modified posttranscriptionally. For example, a 7-methyl-guanosine "cap" is attached to the 5-terminal end of the mRNA through a triphosphate linkage by guanylyl-transferase. A long poly-Atail—not transcribed from the DNA—is attached to the 3 -end of most mRNAs. Many eukaryotic mRNAs also contain introns that must be removed to make the mRNA functional. Their removal requires small nuclear RNAs. 

Kozak, M. (1988). Leader length and secondary structure modulate mRNA function under conditions of stress. Mol. Cell. Biol. 8 2737-2744. 

Prokaryotic mRNAs function in translation with no processing, whereas a very complex process is used by eukaryotes to produce a mature, functional mRNA. 

Prokaryotic mRNAs function in translation with no processing. 

Inhibition of viral mRNA function Inhibition of viral DNA replication via the inhibition of specific polymerases Inhibition of low molecularweight polypeptide gene products... 

Maquat, L. E., and G. G. Carmichael. 2001. Quality control of mRNA function. Cell 104 173-176. 

Messenger RNA (mRNA) functions as a carrier of genetic information from the DNA of the cell nucleus directly to the cytoplasm, where protein synthesis takes place. The bases of mRNA are in a sequence that is complementary to the base sequence of one of the strands of the nuclear DNA. In contrast to DNA, which remains intact and unchanged throughout the life of the cell, mRNA has a short lifetime—usually less than an hour. It is synthesized as needed and then rapidly degraded to the constituent nucleotides. 

Since metals are involved in so many cellular processes, metal bioavailability becomes paramount in understanding how metal ions might affect gene expression at many levels, ranging from signal transduction, transcription factor action, mRNA function, and protein activity. Recent advances in understanding how cells transport metals will be addressed in this review. 

The function of the cap group on mRNAs and presumably, therefore, of the cap recognition proteins has been probed by the construction of mRNAs with altered structures, as well as by analysis of mRNA function in poliovirus-infected cell extracts which lack capbinding activity. Morgan and Shatkin (1980) and Kozak (1980a,ft) prepared reovirus mRNAs with reduced secondary structure by sub-... 

Weber, L. A., Hickey, E. D., Nuss, D. L., and Baglioni, C., 1977, 5 -Terminal 7-methylguanosine and mRNA function Influence of potassium concentration on translation in vitro, Proc. Natl. Acad. Sci. USA 72 318. 

In order to demonstrate that the inhibitory property of vaccinia virus in vitro transcripts is RNA, we subjected these preparations to alkaline hydrolysis, and micrococcal nuclease digestion. The resulting hydrolysate and digest no longer had an inhibitory effect on HeLa cell mRNA function indicating that the integrity of the transcripts is necessary for this inhibition (Coppola and Bablanian, 1983). 

Fig. 7. Effect of vaccinia virus-associated and virion-transcribed RNA on cellular and early viral mRNA function in messenger-dependent reticulocyte lysates. Total cytoplasmic extract of HeLa (20 jLg lane 4), Chinese hamster ovary (CHO 10 fxg lane 7), or vaccinia virus-infected Chinese hamster ovary cells (VCHO 4 fxg lane 10) were used to program 25 jl1 assays. As indicated, 1 fig of vaccinia virus RNA obtained from an in v/7ro-synthesizing reaction (T lanes 5, 8, and 11) or extracted from purified virus (E lanes 6, 9, and 12) was added in combination with the above amounts of RNA from cytoplasmic extracts. The control lanes (1, 2, and 3) contained no exogenous RNA, 1 xg of T, or 1 ig of E, respectively. The products of the nuclease-treated and exogenously-programmed reticulocyte lysates labeled with [ S]methionine (20 xl samples) were subjected to 7.5-15% polyacrylamide-gel electrophoresis and autoradiography. From Coppola and Bablanian (1983).

There are some exceptions to the norm of DNA-dependent DNA or RNA synthesis, mostly in lower eukaryotes or viruses (Fig. 5). One example is RNA-dependent RNA synthesis in plant, animal, or bacterial viruses. In these cases, a single-stranded RNA template rather than double-stranded DNA guides synthesis of the complementary RNA strand, based on conventional base pairing. The polarity of RNA adds a level of complexity during synthesis. Thus, the RNA genome of a virus that can be directly read and thus provides the mRNA function is called the positive strand, as in polio vims. In this case, the viral genome RNA functions as the mRNA and encodes the RNA polymerase, which is synthesized like other viral proteins in the infected cell. This RNA polymerase subsequently synthesizes the complementary... 

The amino acid codons represent a prescription for pairing between molecules of tRNA—with their attached amino acids—and molecules of mRNA. Functionally, the code works via antiparallel pairing of codon and anticodon in an RNA species. Translation into polypeptides is directed only by those triplet nucleotides which lie between the start and stop signals in an mRNA molecule. The corresponding complementary regions in DNA are the structural genes which are transcribed into mRNA by RNA polymerase. 

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