Oat phytochrome a mRNA degradation appears to occur via two distinct

Abstract

We have identified possible mechanisms for the degradation of oat phytochrome A (PHYA) mRNA. The majority of PHYA mRNA molecules appeared to be degraded prior to removal of the poly(A) tail, a pathway that differs from that reported for the degradation of other eukaryotic mRNAs. Polyadenylated PHYA mRNA contained a pattern of putative degradation products that is consistent with a 5′→3′ exoribonuclease, although the participation of a stochastic endoribonuclease cannot be excluded. The poly(A) tail of PHYA mRNA was heterogeneous in size and ranged from ∼14 to 220 nucleotides. Early PHYA mRNA degradation events did not appear to involve site-specific endoribonucleases. Approximately 25% of the apparently full-length PHYA mRNA was poly(A) deficient. Oat H4 histone, β-tubulin, and actin mRNA populations had lower amounts of apparently full-length mRNAs that were poly(A) deficient. Degradation of the Poly(A)-deficient PHYA mRNA, a second pathway, appeared to be initiated by a 3′→5′ exoribonucleolytic removal of the poly(A) tail followed by both 5′→3′ and 3′→5′ exoribonuclease activities. Polysome-associated RNA contained putative PHYA mRNA degradation products and was a mixture of polyadenylated and deadenylated PHYA messages, suggesting that the two distinct degradation pathways are polysome associated.