Regulated 3? processing of histone mRNA requires both the U7 snRNP and a heat-labile component with interesting properties

Abstract

U7-snRNA is an essential component of the RNA processing machinery which generates the 3′ end of mature histone mRNA in the sea urchin. U7-snRNP is classified as a member of the Sm-type U-snRNP family by virtue of its recognition by both anti-thrimethylguanosine and anti-Sm antibodies. We have analyzed the function/structure relationship of the U7-snRNP by mutagenesis experiments. These suggest that the U7-snRNP particle of the sea urchin has three important domains. 1. The 5′ terminal sequences, nucleotides 1–9, are accessible to micronuclease while the remainder of the RNA is highly protected and hence presumably bound up with proteins. The complementarities of the U7-RNA 5′ terminal sequences to the histone pre-mRNA are of functional importance. 2. Nucleotides 9–20 contain a sequence mediating Sm-protein binding. The complementarities between the U7-RNA sequences in this region and the terminal palindrome of the histone mRNA appear to be fortuitous and play only a minor, if any, role in 3′ processing. 3. The terminal palindrome of U7-RNA must be maintained as structure in order for the U7-RNP to work, but its sequence can be drastically altered without any observable effect on snRNP assembly or in 3′ processing.