1. Supplementary Figure S1 (A) Change of reporter activity levels after actinomycin D treatment. HEK293T cells were transiently transfected with the reporter and incubated with actinomycin D for the indicated times. (B) Schematic presentation of deletion constructs of mcry1 3UTR and their reporter activity. (C) Change of reporter mRNA levels after actinomycin D treatment. NIH3T3 cells were transiently transfected with the reporter and incubated with actinomycin D for the indicated times. (D) Each 3UTR in vitro transcribed with 32- α P-rUTP was subjected to in vitro binding and UV cross-linking assay with HEK 293T nuclear extract. The arrow indicates the proteins that shows differential binding. (E) wt 3UTR in vitro transcribed with 32- α P-rUTP was subjected to in vitro binding and UV cross-linking assay with HEK 293T cytoplasmic extract and unlabeled cold wtUTR. The arrow indicates the proteins that shows differential binding. (F) Each 3UTR in vitro transcribed with 32- α P-rUTP was subjected to in vitro binding and UV cross-linking assay with NIH-3T3 cytoplasmic extract. The arrow indicates the proteins that shows differential binding. (G) wt 3UTR in vitro transcribed with 32- α P-rUTP was subjected to in vitro binding and UV cross-linking assay with HEK 293T cytoplasmic extract and homo-oligoribonucleotide A, C, and U. The arrow indicates the proteins that shows differential binding. (H) Alignment of conserved U-tract sequences among various species compared with between 252 and 280 in mcry1 3'UTR.

2. 020406080100120 NAT activity pcNAT pcNAT_wt610 pcNAT_N201 pcNAT_N401 610 mcry1_3UTR 201 401 1 CMVNAT Woo et al_ Supplementary Fig. S1 B A C 0 20 40 60 80 100 120 140 Act.D 0h Act.D 5h AANAT activity (%of Act.D 0h) pcNAT pcNAT_wt610 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0246 Time after Act.D [h] pcNAT-N401 pcNAT-N201 Relative mRNA level (aanat/rpl32)

3. homopolymer HEK_cyto ++ ACU ++ mCry1_3UTR 115 90.5 61.5 46.2 37.5 F G Woo et al_ Supplementary Fig. S1 H N401 wt610 N201 NIH_cyto +++ + + + 115 90.5 61.5 46.2 37.8 37.5 N401 wt610 N201 HEK_nuc + + + + ++ 115 90.5 61.5 46.2 + +++ ++ Cold 37.5 wt610 HEK_cyto 115 90.5 61.5 46.2 DE

4. Sequence(5=>3) Endo-mcry1 F CCT TGA AAA GCC TGG GAA AT Endo-mcry1 R TCC GCT GCG TCT ATA TCC TC Endo-mper2 F GCC TTC AGA CTC ATG ATG ACA GA Endo-mper2 R TTT GTG TGC GTC AGC TTT GG mRPL32 F AAC CCA GAG GCA TTG ACA AC mRPL32 R CAC CTC CAG CTC CTT GAC AT aanat F TTT GAG ATT GAG CGC GAA G aanat R TCG AAC CAG CCC AGT GAC mGAPDH F GCC ATC AAT GAC CCC TTC ATT mGAPDH R GCT CCT GGA AGA TGG TGA TGG mTBP F CAG CCT TCC ACC TTA TGC TC mTBP R TTG CTG CTG CTG TCT TTG TT Supplementary Table primer sequences for real time PCR