Using cDNA probes, we have analysed the sequence complexity and the frequency distribution of the polysomal poly(A)‐containing RNA from neuroblastoma cells at two different developmental states: either as round, immature neuroblasts, or as differentiated cells exhibiting the morphological properties of mature neurons. The total complexities measured for mRNA from undifferentiated and differentiated cells are identical and correspond to approximately 7000 average‐sized sequences of 1750 nucleotides distributed in the same three abundance classes. We have determined the homology between the mRNA populations corresponding to the two developmental states by heterologous cross‐hybridization: all the sequences from differentiated cells are present in the polysomes of undifferentiated cells. Conversely, the mRNA from differentiated cells fails to hybridize with about 15% of hybridizable cDNA corresponding to undifferentiated cells. This difference probably results from the disappearance of some mRNA species and may be related to the terminal differentiation of neuroblastoma cells.

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Determination of the molecular weight of valyl and isoleucyl tRNA synthetases under denaturing conditions leads to the conclusion that both enzymes are made of a single polypeptide chain of a molecular weight of 110000 approximately. The presence of one amino acid binding site per chain was determined by equilibrium dialysis.

We have analysed the poly(A)-containing RNA from neuroblastoma cells at two different developmental states : either as round, immature neuroblasts grown in suspension, or as differentiated cells exhibiting the morphological properties of mature neurons, when attached to a culture dish.Suspension-grown and monolayer cells were pulse-labelled with tritiated uridine. The profile of cytoplasmic poly(A)-containing RNA from suspension cells is highly heterogeneous with peaks ranging from 16-30 S. The profile obtained from differentiated cells appears somewhat distinct from the previous one. This is evidenced by a relative decrease in the 26-S peak and a virtual disappearance of the 16-S component.In order to compare the 'steady-state' patterns of poly(A)-containing RNA in these two developmental stages, polysomal RNA was prepared from unlabelled cells. Following sucrose gradient sedimentation, each fraction was hybridized to [3H]poly(U). Examination of the two RNA hybridization profiles reveals striking similarities suggesting that 'steady-state' messenger populations include, on the average, the same subspecies. The 16-S fraction, which was not observed after the pulse-labelling of the monolayer culture, is detected here by hybridization to [3H]poly(U) when using polysomal poly(A)-containing RNA from monolayer cells as substrate.These results suggest that terminal differentiation of neuroblastoma cells is not accompanied by major alterations of the transcription program and is paralleled by a marked stabilization of the 16-S species.Mouse neuroblastoma cells provide a useful tool to study the acquisition of neuronal properties in tissue culture. The cell lines can generally be cultured under two different developmental states : either as round, immature neuroblasts grown in suspension, or as differentiated cells exhibiting the morphological properties of mature neurons, when attached to a culture dish.Eventual changes in the pattern of specific proteins accompanying morphological differentiation have been widely explored ; generally speaking no striking difference has been noticed in the spectrum of newly synthesized proteins constituting, from a quantitative stand point, the major species of the cell (C. Vimard and L. Legault-Demarre, personal communication) except perhaps in the compartment of high-molecular-weight proteins that could possibly represent membrane components [2]. Likewise, the rate of synthesis of tubulin [3], one main protein phate.Abbreviation. BtZcAMP, dibutyryl adenosine 3' : S'-monophoselement of the cell neurities, was found not to vary appreciably in the course of differentiation. By contrast several reports have emphasized rate variations in the synthesis of acetylcholinesterase [4], 14.3.2 protein [5] or of the neurotransmitter-forming enzymes [6,7]. Little is known, however, about ~ the mechanisms involved in the control of genetic expression during the development of neuronal traits in tissue culture conditions. Recent work from Littauer et al. [8] based upon the use of dimethylsulfoxide...