Insertion in the second exon, within coding sequences. Transcription in this mutant initiates within the P-element, just downstream of the 3' end of the w sequences. Translation is predicted to begin at the last three nucleotides of P-element sequence and continue in-frame into nbs sequences. In the predicted translation product, the first residue of the first BRCT domain is changed from Leu to Met, but the domain is otherwise intact. The nbs N-terminal FHA domain is missing in this product as the insertion occurs downstream of the sequence coding this domain.
nbs1/nbsEY15506 larvae are hypersensitive to gamma irradiation compared to controls. Homozygous larvae are also sensitive to gamma irradiation compared to controls, but are significantly less sensitive than nbs1/nbsEY15506 larvae at doses higher than 500 rads.
Homozygotes have a normal G2/M DNA damage-dependent cell cycle checkpoint induced by irradiation at high-dose (4000 rads). At low-dose irradiation (1000 rads) the checkpoint is significantly reduced compared to wild type.
nbs1/nbsEY15506 larvae show loss of the G2/M DNA damage-dependent cell cycle checkpoint at low-dose irradiation (1000 rads) and a significant weakening of the checkpoint at high-dose irradiation (4000 rads).