In vitro nuclear transport of ribosomal ribonucleoprotein: temperature affects quantity but not quality of exported particles.

Abstract

The in vitro export of ribosomal ribonucleoprotein (rRNP) from Tetrahymena nuclei was investigated at the optimal growth temperature of 28°C and at the nonlethal temperature of 8°C. At both temperatures, nuclei exported ribosomal precursor particles that revealed the same physical qualities of size, appearance in negative-staining electron microscopy, sedimentation coefficient, buoyant density, and rRNA pattern. Surprisingly, fewer rRNP particles were exported at 8 than at 28°C, as was revealed by a lower saturation plateau in the export kinetics from nuclei prelabeled with [3H]uridine. Upon a temperature increase from 8 to 28°C, additional rRNP particles were exported. We conclude that nuclei export only a defined portion of rRNP particles at a given temperature, although enough potentially transportable rRNP particles are present in nuclei. Obviously, the reactivity of at least one of the reactants involved directly or indirectly in rRNP export changes with temperature.

Nucleocytoplasmic RNA transport

“…Subsequent work from a number of laboratories has demonstrated that regulated RNA transport proceeds in vitro after detergent treatment (119,(123)(124)(125)(126), and hybridization properties of released poly(A)q-RNA closely resemble those of cytoplasmic poly(A)+ mRNA (126). Detergent treatment does not affect the temperature dependence of the transport process (119), which also appears to be unaffected by phase transitions of nuclear membranes (119,125), at least in mammalian systems, although somewhat different results have been obtained with Tetrahymena (127). We have found that a detergent treatment is mandatory to remove cytoplasmic contamination (see below).…”

Thermal down‐regulation of exportable rRNA in nuclei

“…Recently, we have shown in nuclei isolated from Tetrahyrnena Wunderlich et al, 1983) that temperature elevation from 8°C to 28"C, under export conditions, induces a gradual increase in the maximum rRNP export, i.e. the fraction of rRNP particles that can be maximally exported from nuclei gradually increases with increasing temperatures (cf.…”

“…: 50 Cihmol; NEN-chemicals, Frankfurt, F.R.G.) according to one of the procedures described in detail by Herlan et al (1980) or Wunderlich et al (1983).…”

“…The conditions of rRNA export were detailed previously (Herlan et al, 1980;Wunderlich et al, 1983). In brief, nuclei prelabeled with 3H-uridine were suspended in ST at 0°C.…”

“…also and can export precursor ribosomal ribonucleoprotein (rRNP) particles (Herlan et al, 1980). These nuclei possess a specific temperature-sensitive export mechanism: It determines the number of rRNP particles that can be maximally exported from the potentially exportable nuclear rRNP particles out of nuclei at a given temperature Wunderlich et al, 1983). The present data suggest the existence of another temperature-sensitive mechanism that affects the number of the potentially exportable rRNP particles inside nuclei.…”