A cross-cultural comparison of sleep duration between U.S. and Australian adolescents: the effect of school start time, parent-set bedtimes and extracurricular load

STUDY OBJECTIVE: To test whether sleep duration on school nights differs between adolescents in Australia and the U.S. and, if so, whether this difference is explained by cultural differences in school start time, parental involvement in setting bedtimes and extra-curricular commitments. PARTICIPANTS: 385 adolescents aged 13-18 years (M=15.57,SD=0.95; 60% male) from Australia and 302 adolescents aged 13-19 years (M=16.03, SD=1.19; 35% male) from the United States. METHODS: Adolescents completed the School Sleep Habits Survey during class time, followed by an 8-day Sleep Diary. RESULTS: After controlling for age and sex, Australian adolescents obtained an average of 47 minutes more sleep per school night than those in the U.S. Australian adolescents were more likely to have a parent-set bedtime (17.5% vs 6.8%), have a later school start time (8:32am vs 7:45am) and spend less time per day on extra-curricular commitments (1h37m vs 2h41m) than their U.S. peers. The mediating factors of parent-set bedtimes, later school start times, and less time spent on extra-curricular activities were significantly associated with more total sleep. CONCUSIONS: In addition to biological factors, extrinsic cultural factors significantly impact upon adolescent sleep. The present study highlights the importance of a cross-cultural, ecological approach and the impact of early school start times, lack of parental limit setting around bedtimes and extracurricular load in limiting adolescent sleep

The terminal redundant regions of bacteriophage T7 DNA: their necessity for phage production studied by the infectivity of T7 DNA after modification by various exonucleases

Dreiseikelmann B, Wackernagel W. The terminal redundant regions of bacteriophage T7 DNA: their necessity for phage production studied by the infectivity of T7 DNA after modification by various exonucleases. Molecular and General Genetics. 1978;159(3):321-328.Some aspects of the involvment of the terminal reduntant regions of T7 DNA on phage production have been studied by transfection experiments with T7 DNA after treatment of the molecules with [lambda] exonuclease or [lambda] exonuclease plus exonuclease I. It was found that terminal 5prime gaps between 0.08 and 6.4% of the total length did not decrease the infectivity of the molecules although such gaps cannot be filled directly by DNA polymerases. Rather, compared to fully native DNA the infectivity of gapped DNA increased up to 20 fold in rec + spheroplasts and up to 4 fold in recB spheroplasts. This indicates a protective function of the single-stranded termini against the recBC enzyme in rec + and possibly another unidentified exonuclease present also in recB. The possibility that spontaneous circularization of the gapped molecules in vivo provides protection against exonucleolytic degradation was tested by transfection with T7 DNA circularization in vitro by thermal annealing. Such molecules were separated from linear molecules by neutral sucrose gradient centrifugation. They displayed a 3 to 6 fold higher infectivity in rec + and recB compared to linear gapped molecules, which shows that T7 phage production may effectively start from circular DNA. When the 3prime single-stranded ends from gapped molecules were degraded by treatment with exonuclease I the infectivity of the molecules was largely abolished in rec + and recB as soon as 40 to 80 base pairs had been removed per end. It is concluded that the terminal regions of T7 DNA molecules are essential for phage production and that the redundancy comprises probably considerably less than 260 base pairs. The results are discussed with respect to the mode of T7 DNA replication