mRNA decay rates in late-developing Dictyostelium discoideum cells are heterogeneous, and cyclic AMP does not act directly to stabilize cell-type-specific mRNAs.

We reevaluated the use of 32PO4 pulse-chases for analyzing mRNA decay rates in late-developing Dictyostelium cells. We found that completely effective PO4 chases could not be obtained in developing cells and that, as a consequence, the decay rates exhibited by some mRNAs were influenced by the rates at which they were transcribed. In developing cells disaggregated in the presence of cyclic AMP, the poly(A)+ mRNA population turned over with an apparent half-life of 4 h, individual mRNA decay rates were heterogeneous, and some prestalk and prespore mRNAs appeared to decay with biphasic kinetics. In cells disaggregated in the absence of cyclic AMP, all prestalk and prespore mRNAs decayed with biphasic kinetics. During the first 1 to 1.5 h after disaggregation in the absence of cyclic AMP, the cell-type-specific mRNAs were selectively degraded, decaying with half-lives of 20 to 30 min; thereafter, the residual prestalk and prespore mRNA molecules decayed at rates that were similar to those measured in the presence of cyclic AMP. This short-term labilization of cell-type-specific mRNAs was observed even for those species not requiring cyclic AMP for their accumulation in developing cells. The observation that cell-type specific mRNAs can decay at similar rates in disaggregated cells with or without cyclic AMP indicates that this compound does not act directly to stabilize prestalk and prespore mRNAs during development and that its primary role in the maintenance of cyclic-AMP-dependent mRNAs is likely to be transcriptional

Nanosecond decay studies of a fluorescence probe bound to apomyoglobin.

Excited state interactions of N-(p-tolyl)-2-aminonaphthalene-6-sulfonate (2, 6 p-TNS) bound to apomyoglobin were studied by nanosecond time-resolved emission spectroscopy. A dynamic interaction of the excited dye molecule with its binding site, associated with a significant change in the emission energy with time, was observed. The decay kinetics were found to be complex and consistent with the kinetic model for solvent relaxation as proposed by Bakhshiev et al. (Opt. Spectrosc. 21:307. 1966). The behavior of 2, 6 p-TNS bound to apomyoglobin was found to be qualitatively similar to that of the dye dissolved in a viscous solvent such as glycerol or adsorbed to egg lecithin vesicles. The detailed information obtained by following the changes in emission spectra of fluorescent probes on the nanosecond time scale leads to a better understanding of their interactions with biological systems