Nelfb (negative elongation factor complex member B) encodes one of four subunits of negative elongation factor (NELF) that together function to cause transcriptional pausing of RNA polymerase II. These conditional knock-out mice possess loxP sites flanking the first four exons of the Nelfb gene. Mice that are homozygous for the targeted mutation are viable and fertile. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have the first four exons deleted in cre-expressing tissues creating a null allele. Genetic disruption of Nelfb results in the destabilization of the entire NELF complex and a genome-wide loss of transcriptional pausing. These mice may be useful for studying cellular regulation by transcriptional pausing. When bred to oocyte-expressing Tg(Zp3-Cre)93Knw mice (Stock No. <a href="https://www.jax.org/strain/003651"">003651</a>), resulting Nelfb-deficient embryos fail to develop past early implantation with 100% penetrance of embryonic lethality. ES cells derived from mice homozygous for the conditional allele, senesce following Cre recombinase exposure.

NELF-BFL conditional knock-out mice possess loxP sites flanking exons 1-4 of the Nelfb gene and may be useful for studying cellular regulation by transcriptional pausing.

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