Mammalian messenger RNA

Table 38-1. The genetic code (codon assignments in mammalian messenger RNA)J...

Inacio A, Liebhaber SA (2003), Pathways of mammalian messenger RNA degradation, In Makrides SC (Ed.), Gene Transfer and Expression in Mammalian Cells, Elsevier Science BV, Amsterdam, pp. 495-512. 

Which one of the following statements correctly describes the synthesis of mammalian messenger RNA (mRNA) ... 

Which of the following most correctly describes mammalian messenger RNAs ... 

Bacterial and Mammalian Messenger RNA RNA Polymerase 118 Nuclear Heterogeneous RNA— A Precursor of Mammalian Messenger RNA 121 Visualization of Transcription 122... 

As we shall see later, viral, bacterial, and mammalian messenger RNA s have been isolated. But before we can discuss their preparation, we must review some of the properties of the enzyme catalyzing DNA transcription—RNA polymerase. 

Brawerman, G., 1981, The role of the poly(A) sequence in mammalian messenger RNA, Crit. Rev. Biochem. 10 1. 

Ara-A is phosphorylated in mammalian cells to ara-AMP by adenosine kinase and deoxycytidine kinase. Further phosphorylation to the di- and triphosphates, ara-ADP and ara-ATP, also occurs. In HSV-1 infected cells, ara-A also is converted to ara-ATP. Levels of ara-ATP correlate directly with HSV rephcation. It has recently been suggested that ara-A also may exhibit an antiviral effect against adenovims by inhibiting polyadenylation of viral messenger RNA (mRNA), which may then inhibit the proper transport of the viral mRNA from the cell nucleus. 

STATs (signal transducers and activators of transcription) transmit signals primarily from cytokines (see Chapter 6).36 Seven mammalian stat genes have been identified up to now and localized on chromosomes. Splicing of the pre-messenger RNA may lead to additional variants. STAT 2 participates (jointly with STAT 1) only in IFN-cc/p signalling.3T STAT 2 is present in nearly all cells, whereas the distribution of STAT 4 and STAT 5 is more restricted. STAT 4 is expressed in myeloid cells, where it is induced by IL-4 signals and where it participates in early myeloid differentiation.38,39 STATs have... 

Minocycline, a tetracycline, is indicated in syphilis or gonorrhea in patients sensitive to penicillin. In addition, it may be used in uncomplicated urethral, endocervical, or rectal infection, and in uncomplicated gonococcal urethritis in men (see also Figure 96). Tetracyclines enter bacterial cells by both passive diffusion and active transport, and then accumulate intraceUularly. This does not occur in mammalian cells. The tetracyclines bind to the 308 subunit of the bacterial ribosome in such a way that the binding of the aminoacyl-transfer RNA to the acceptor site on the messenger RNA ribosome complex is blocked (see Figure 96). 

Since the discovery by Hadjivassiliou and Brawerman (1966) that rat liver microsomes contain polyadenylic acid [poly(A)] sequences, there has been much recent evidence which indicates that a high proportion of the messenger RNA s (mRNA s) of mammalian cells contain poly(A) sequences which are covalently linked to the mRNA molecule. Most of the rapidly labeled nonribosomal RNA components of mouse sarcoma 180, HeLa, and L cell polysomes have been shown to contain adenylate-rich sequences (Lee et at, 1971 Edmonds et al., 1971 Darnell et at, 1971a Sheldon et at, 1972 Perry et al., 1972). 

While the poly (A) sequences do seem to be involved in the transport of mRNA s from the nucleus, this does not seem to be the sole function of the poly (A) tract for example, adenovirus DNA appears to lack a DNA sequence complementary to poly (A) but replicates in the nucleus of the mammalian cell and appears to have a poly (A) tract added to the viral mRNA by host-cell mechanisms for transport of the adenovirus mRNA to the cytoplasm (Philipson et ah, 1971). As with cellular messages, cordycepin blocks both the labeling of the poly (A) tracts and the appearance of adenovirus-specific RNA in the cytoplasm of infected cells (Philipson et ah, 1971). In contrast, vaccinia virus replicates exclusively in the cytoplasm of cells it infects and still contains poly(A) sequences (Kates, 1970). Since no role in transport is involved here, it suggests that some mRNAs may require a poly (A) sequence for proper translation. Further, not all mammalian mRNAs contain poly (A) and still are transported to the cytoplasm for translation. Specifically, the 9 S histone message isolated by Adesnik and Darnell (1972) from HeLa cells lacks any detectable poly (A) sequence of any significant length. These workers have also shown that the exit time of the histone mRNA molecule from the nucleus is shorter than that of other messenger RNA s. 

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