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Cellular and physiological evidence suggests the presence of a novel class of systemically mobile plant molecules that are recognized by antibodies against vertebrate atrial natriuretic peptides (ANPs). In order to characterize the function of these immunoanalogues we have expressed the full-length recombinant (AtPNP-A[1–126]) and demonstrate that this molecule induces osmoticum-dependent H2O uptake into protoplasts at nanomolar concentrations and thus affects cell volume. A similar response is also seen with a recombinant that does not contain the signal peptide (AtPNP-A[26–126]) as well as a short domain (AtPNP-A[33–66]) that shows homology to the vertebrate peptide. Taken together, these findings suggest that AtPNP-A has an important and systemic role in plant growth and homeostasis. [Copyright &y& Elsevier]

The pulse-chase experiments with Friend erythroleukemia cells designed to reveal the metabolic properties of the protein complex of 40-S particles showed that the major polypeptides of this complex turn over with half-lives between 19 h and 206 h. The main conclusion from the experiments is that the complex does not degrade as a single unit. Since the individual polypeptides forming the complex live much longer than hnRNA, and in addition degrade at a different rate, we considered the following two modes of degradation as most likely. (1) The complex might not be subjected to a profound degradation at the end of the processing of associated pre-mRNA. In this case it should exist as a long-lived recyclable mosaic of metabolically differing polypeptides whose replacement takes place at a specific rate. (2) Alternatively, the protein complex might be completely degraded at the end of processing, but in a way that liberates free individual polypeptides available for recycling. The further experiments indicate that the 37 000-Mr, 34000-Mr and 32 000-Mr core proteins in isolated 40-S particles and in particles associated with a nuclear fraction released from chromatin after micrococcal nuclease digestion degrade at different rates. These experiments suggest the existence of at least a metabolic heterogeneity among the population of nuclear particles carring pre-mRNA. [ABSTRACT FROM AUTHOR]

In a previous paper in this journal [Djondjurov, L., Ivanova, E. and Tsanev, R. (1979) Eur. J. Biochem. 97, 133–139], we showed that a nuclear fraction released from chromatin under a mild nuclease digestion contained an increased amount of hnRNA and the bulk of nonhistone proteins with a high metabolic rate. The present investigation has revealed that the nonhistone proteins of this fraction could be divided into three distinct metabolic groups. The first group consists of proteins with a fast turnover rate (mean half-life 30 min) which migrate into chromatin immediately after their synthesis. These proteins are predominantly acid-soluble and have relatively high molecular weights. The second group includes proteins which migrate to the nucleus more slowly and metabolize with a moderate turnover rate (mean half-life 5 h). The third group contains proteins with a more conservative metabolic behaviour. In experiments with actinomycin D it was found that the bulk of the nonhistone proteins of this fraction are not real components of the chromatin but belong to the protein moiety of heterogeneous nuclear ribonucleoprotein particles associated with chromatin. [ABSTRACT FROM AUTHOR]