The new RENT family of repetitive elements in Nicotiana species harbors gene regulatory elements related to the tCUP cryptic promoter

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Abstract
The tCUP cryptic constitutive promoter was discovered in the tobacco genome by T-DNA (transfer DNA) tagging with a promoterless GUS–nos gene. Here, we show that the portion of the tCUP sequence containing a variety of cryptic gene regulatory elements is related to a new family of moderately repetitive sequences (102 copies), the RENT (repetitive element from Nicotiana tabacum) family. The RENT family is found only in certain Nicotiana species. Five RENT elements were cloned and sequenced. The RENT elements are a minimum of 5 kb in length and share 80–90% sequence similarity throughout their length. The 5' termini are the same in the isolated RENT family members and are characterized by a conserved border sequence (TGTTGA(T or C)ACCCAATTTT(T or C)). The 3' ends of RENT sequence similarity vary in location and sequence. The tCUP cryptic promoter originated from a unique truncated RENT element that interrupts a phytochelatin synthase-like gene that may have undergone rearrangements prior to or resulting from T-DNA insertion. No evidence was found for expressed coding regions within the RENT elements; however, like the cryptic gene regulatory elements within the tCUP sequence, the isolated RENT elements possess promoter activity and translational enhancer activity.Key words: cryptic promoter, Nicotiana, T-DNA, translational enhancer, repetitive element.