Relationship between nuclear and cytoplasmic poly(adenylic acid).

Abstract

The kinetics of accumulation of radioactive poly(A) in the nucleus and cytoplasm of mouse L cells have been determined using labeling conditions in which the cellular ATP pool is shown to have a nearly constant specific radioactivity. Most or all nuclear poly(A) accumulates with kinetics very similar to those of heterogeneous nuclear RNA, having a half-time of about 25 min. There is little or no lag before attainment of a maximal rate of accumulation of cytoplasmic poly(A). These data are consistent with a variety of models in which nuclear poly(A) does or does not all serve as a precursor of cytoplasmic poly(A). In either type of model there must be a class of poly(A) either synthesized in the cytoplasm or passing through a small nuclear pool separate from the main pool of nuclear poly(A). The T3' ends of many messenger RNA (mRNA) and heterogeneous nuclear RNA (hnRNA) molecules are polyadenylated posttranscriptionally. This observation has led to the suggestion that polyadenylated hnRNA molecules serve as precursors of mRNA (1). If the 3' ends of all polyadenylated hnRNA molecules were precursors of mRNA, these nuclear precursors could easily be selected from total hnRNA by affinity chromatography (2). If some polyadenylated hnRNA molecules decay entirely in the nucleus, such selection would not serve to isolate only precursors of mRNA. In the latter instance, some poly(A) would be expected to decay in the nucleus.Jelinek et al. (3) have presented evidence that most or all cytoplasmic poly(A) is derived from nuclear poly(A), and suggest that nuclear poly(A) may be conserved. More recently Perry, Kelley, and LaTorre (4) reported on their investigations of the kinetics of accumulation of poly(A) in the nucleus and cytoplasm of L cells and concluded that some nuclear poly(A) must decay in the nucleus and that substantial synthesis of cytoplasmic poly(A) may occur. Our investigations of ATP pools and nuclear RNA in L cells (5, 6) gave us reason to think that there might be sources of error in the investigations of Perry et al. (4). Perry et al. demonstrated that total cellular RNA labeled with tritiated adenosine at high concentration accumulates with kinetics indicating that it is synthesized via an ATP pool of constant specific radioactivity. Whereas, this appears to be valid over the long term, their argument cannot be convincingly applied over the first few hours, because it does not take into account the rapid initial accumulation of highly unstable hnRNA and nuclear precursors of ribosomal RNA, nor the extensive conversion of adenine nutleotides to guanine nucleotides under the labeling conditions used (5, 6). In the investigations of Perry et al. (4) the cellular ATP pool would not reach a constant specific radioactivity until as late as 2 hr after the addition of exogenous label (Brandhorst, unpublished observations); this could seriously distort the actual kinetics of accumulation of poly(A). As explained previously (4, 6), rapid establishment of constant specific activity of the ATP pool facilita...

Ribonucleic acid synthesis in isolated Drosophila nuclei

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Preparation and Characterization of Candidate Reference Materials for Telomerase Assays

“…The spectrophotometric value for the total RNA was divided by the number of cells used in the extraction to determine the amount of RNA per cell. The resulting range (3-9 pg) is within the range (5-30 pg) reported previously (16 ). The CV (71%) was greater for the measurement of total RNA than for real-time PCR (2%).…”

The stability, polyadenylic acid content and ribonucleoprotein form of nulcear ribonucleic acid in artichoke

“…Somne of the hnRNA is polyadenylated, the proportion showingsome variation between the two different physiological states of the tubers used in these experiments (Table 4). The proportion of poly(A)-containing hnRNA is rather similar to that reported in animal cells (Greenberg & Perry, 1972;Brandhorst & McConkey, 1975;Lewin, 1975), The rates of turnover of poly(A)-containing hnRNA and hnRNA lacking poly(A) appear to be identical. This similarity, and the value for the half-life of the hn-RNA, is comparable with the results reported for mouse L cells by Brandhorst & McConkey (1974, 1975.…”