Measurement of the gamma ray background in the Davis Cavern at the Sanford Underground Research Facility

Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from γ-rays emitted by 40K and the 238U and 232Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4,850-foot level. In order to characterise the cavern background, in-situ γ-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0--3300~keV) varied from 596~Hz to 1355~Hz for unshielded measurements, corresponding to a total flux in the cavern of 1.9±0.4~γ cm−2s−1. The resulting activity in the walls of the cavern can be characterised as 220±60~Bq/kg of 40K, 29±15~Bq/kg of 238U, and 13±3~Bq/kg of 232Th

KDEL and KKXX Retrieval Signals Appended to the Same Reporter Protein Determine Different Trafficking between Endoplasmic Reticulum, Intermediate Compartment, and Golgi Complex

Many endoplasmic reticulum (ER) proteins maintain their residence by dynamic retrieval from downstream compartments of the secretory pathway. In previous work we compared the retrieval process mediated by the two signals, KKMP and KDEL, by appending them to the same neutral reporter protein, CD8, and found that the two signals determine a different steady-state localization of the reporter. CD8-K (the KDEL-bearing form) was restricted mainly to the ER, whereas CD8-E19 (the KKMP-bearing form) was distributed also to the intermediate compartment and Golgi complex. To investigate whether this different steady-state distribution reflects a difference in exit rates from the ER and/or in retrieval, we have now followed the first steps of export of the two constructs from the ER and their trafficking between ER and Golgi complex. Contrary to expectation, we find that CD8-K is efficiently recruited into transport vesicles, whereas CD8-E19 is not. Thus, the more restricted ER localization of CD8-K must be explained by a more efficient retrieval to the ER. Moreover, because most of ER resident CD8-K is not O-glycosylated but almost all CD8-E19 is, the results suggest that CD8-K is retrieved from the intermediate compartment, before reaching the Golgi, where O-glycosylation begins. These results illustrate how different retrieval signals determine different trafficking patterns and pose novel questions on the underlying molecular mechanisms