CLOCK (Circadian Locomotor Output Cycles Kaput)

Overview

The CLOCK gene encodes a central transcription factor that controls the circadian rhythm – the 24-hour sleep-wake cycle. Together with BMAL1, it forms the core of the molecular clockwork in almost every cell of the body.

📍 Position
4q12 (Chromosome 4)

🏷️ Category
Brain

⚡ Function
Transcription Factor (with BMAL1)

📊 Frequency
30-40% carry the C-allele (rs4580704)

Function & Significance

CLOCK is a bHLH transcription factor that forms a heterodimer with BMAL1. This complex binds to E-box elements in the promoters of Period (PER1, PER2, PER3) and Cryptochrome genes (CRY1, CRY2).

The Circadian Feedback Loop:

CLOCK/BMAL1 activate PER and CRY transcription (Day phase)
PER/CRY proteins accumulate in the cytoplasm
PER/CRY migrate back into the nucleus and inhibit CLOCK/BMAL1 (Night phase)
PER/CRY are degraded, and the loop begins anew

💡 Did you know? The circadian rhythm influences not only sleep but also hormone production, metabolism, immune function, and even the effectiveness of medications!

🧬 Genetic Variant

rs4580704
4:56386184

Wild Type

C

/

Variant

T

T3111C in the 3′ UTR: The C-allele is associated with late sleep phases (evening chronotypes, “night owls”), seasonal depression, and delayed sleep phase syndrome.

T/T (Wild Type)
Normal chronotype, typical morning person

C/C or C/T
Tendency towards evening chronotype, delayed sleepiness

⚠️ Clinical Significance:

C-allele carriers have an increased risk of Seasonal Affective Disorder (SAD)
Difficulties adjusting to shift work
Possible Delayed Sleep Phase Syndrome

🕐 Chronotype & Lifestyle

Depending on your genotype, you can optimize your sleep:

T/T (Morning Person)

Optimal: Go to bed early, wake up early
Complete important tasks in the morning
Use morning sunlight for stabilization
Maintain regular sleep times

With C-Allele (Night Owl)

Align schedule with late appointments/activities
Morning light therapy helps
Consider melatonin supplementation
Pay extra attention to light during winter

✅ Tips for all Chronotypes:

Use Zeitgebers: Morning light, fixed meal times, and exercise help stabilize the rhythm
Blue Blockers: Blue light filtering glasses or software in the evening to aid melatonin production
Consistency: Do not shift sleep times by more than 1-2 hours, even on weekends

📚 Data Sources

OMIM: #601851 (CLOCK Gene)
dbSNP: rs4580704
PubMed: Katzenberg et al. (1998) – CLOCK gene polymorphism and diurnal preference
Nature Reviews: Takahashi (2017) – Transcriptional architecture of the mammalian circadian clock

Last Update: February 2026

CLOCK