mRNA in human cells contains sequences complementary to the Alu family of repeated DNA.

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Abstract
Approximately 1/2 of the polysomal poly(A)+RNA from CCRF-CEM human lymphoblastoid cells associates at low R0t (10 M .cntdot. s) [where R0 is the initial concentration of RNA (M) and t is time (s)] to form branched complexes detectable by EM. The complexes typically involve 2-16 molecules associated over double-stranded regions 120 .+-. 30 base pairs long. Apparently, poly(A)+RNA contains repeated-sequence elements that are highly represented in the mRNA population. Hybridization of polysomal poly(A)+RNA with a recombinant human DNA plasmid, p.lambda.H15C, which contains at least 3 regions complementary to 2 different members of the Alu family of DNA repeat sequences, showed a total of 5 regions where R loops are formed. The hybridized regions comprising these groups are 260 .+-. 180, 240 .+-. 170, 150 .+-. 70, 180 .+-. 60 and 180 .+-. 80 base pairs long. Sequences in this recombinant DNA are evidently represented in the mRNA population at different frequencies. The hybridizing sequence of the RNA molecules is located near one terminus in 13% of the R loops and internally in 53% of the R loops. Of the R loops (35%) apparently involve RNA molecules hybridized over the entire length of only 200 .+-. 110 base pairs.