Units of transcription for cytoplasmic RNA in mouse myeloma cells.

The size of transcription units for several of the abundant cytoplasmic mRNA species in mouse myeloma cells has been analyzed by the ultraviolet light mapping technique. Inactivation kinetics and target size analyses for production of the predominant RNA species indicate that the mRNAs originate in precursor molecules that are 2--14 times larger than the mature mRNA. This estimate of the size of the transcription unit may be a minimum one since it would not take into account promoter-distal sequences if these were not necessary for processing of the mRNA precursor.