This study was undertaken to test for differential gene expression in intramuscular adipocytes during fat deposition of feedlot steers. Angus × Hereford steers ( n = 50) were fed a high-energy concentrate ration ad libitum for 20 ( n = 5), 86 ( n = 15), 121 ( n = 15), and 146 days ( n = 15) to obtain various degrees of intramuscular adipocyte development. Carcass traits were significantly different ( P < 0.05) between the groups. Intramuscular adipose tissue was excised from the longissimus dorsi and snap frozen in liquid nitrogen. Pooled samples of total RNA representing each group were analyzed by differential-display polymerase chain reaction using 200 primer combinations comprising 20 arbitrary (5′) and 10 anchor (3′) oligonucleotides. Bands ( n = 70) representing putative differences among treatment groups were excised, sequenced, and subjected to BLAST homology search. From these, 40 contained significant homology to known genes. One was of particular interest, the translational repressor NAT1 (novel APOBEC-1 target-1). NAT1 mRNA was quantified in individual animals to confirm differential expression among treatment groups. Results indicate that NAT1 message is more abundant ( P < 0.05) in intramuscular adipocytes of younger/leaner animals.