Minimum estimate of the lifetime of histone messenger RNA of HeLa cells

Histone mRNAs contain blocked and methylated 5' terminal sequences but lack methylated nucleosides at internal positions

Histone mRNA, labeled with 32P or 3H-methionine during the S phase of partially synchronized HeLa cells, was isolated from the polyribosomes and purified as a "9S" component by sucrose gradient sedimentation. We identified two types of 5' terminals, m7G(5')pppNmpN and m7G(5')pppNm-pNmpN, in which the first methylated nucleoside is 7-methylguanosine, the second is either N6, 2'-O-dimethyladenosine, 2'-O-methyladenosine, or 2'-O-methylguanosine, and the third is 2'-O-methyluridine, 2'-O-methylcytidine, or 2'-O-methyladenosine. Approximately 1.7% of the 32P label was present in the 5' terminal structures. Assuming a similar specific radioactivity for all phosphates, this percentage corresponds to an average of one terminal per 335 nucleotides. Histone mRNA differed from bulk polyadenylylated mRNA of HeLa cells in lacking significant amounts of 2'-O-methyluridine or 2'-O-methylcytidine in the second position of the 5' terminal oligonucleotide and in lacking N6-methyladenosine residues at internal positions.

Further evidence of transcriptional and translational control of histone messenger RNA during the HeLa S3 cycle

Using a translational assay and new analytical procedures we have found that: -Histone mRNA can be detected both associated with polyribosomes and in the postribosomal supernatant of S phase HeLa S3 cells.-Inhibition of DNA replication by cytosine arabinoside treatment causes histone mRNA to completely disappear from polyribosomes, and little histone mRNA can be detected in the postribosomal supernatant of inhibited cells. These data indicate that histone mRNA does not accumulate in the cytoplasm after the inhibition of DNA replication. -Histone mRNA species cannot be detected in the postribosomal supernatant of G1 cells synchronized by selective detachment. This observation, together with the previous finding that histone mRNA is not present on G1 polyribosomes, is consistent with the idea of a transcriptional block in histone mRNA production and transport to the cytoplasm during G1.