Low molecular weight nuclear RNA in human lymphocytes : A comparison of PHA-treated and control cells

Seven species of low molecular weight nuclear (LMN) RNA were identified in human peripheral lymphocytes. These were designated as A, B, C, D, D′, E and F. The same 7 species of LMN RNA were obtained from resting lymphocytes and from lymphocytes exposed to PHA for 16 and 60 h, respectively. Thus, no detectable qualitative changes were seen in the spectrum of LMN RNAs during PHA-induced lymphocyte transformation. However, the amount of species A, D-D′, E and F per nucleus in fully transformed cells was greater than in untreated lymphocytes. This increase had not yet occurred after 16 h treatment with PHA. ³H-Uridine was incorporated into all species of LMN RNA of resting and PHA-treated lymphocytes. Furthermore, all species of LMN RNA except C (5S RNA) were methylated in both resting and transformed cells. The ³H and ¹⁴C specific activities of LMN RNAs following an 8 h exposure to ³H-uridine and ¹⁴C-methyl methionine were higher in PHA-treated cells than in untreated lymphocytes. For several species of LMN RNA (A, D-D′, E, F) the highest ³H and ¹⁴C spec. act. were observed after 16 h exposure to PHA. The possibility that quantitative alterations in the synthesis and methylation of LMN RNAs may occur during lymphocyte transformation is discussed.