How to determine a correct promotor sequence? (Bisulfite sequencing - uni assingment)
I think there is no fixed size. Ideally you would have something like histone ChIP-seq or ATAC-seq data to approximate the relevant upstream interval. Since this is not always possible most people go with -500bp. Others might have different suggestions though. Maybe matching known motifs of transcription factors that regulate that promoter to the upstream region can help approximating a better window. But as Sanger sequencing usually gives about 1kb of sequence I'd just take a 500bp to 1kb window and sequence that, fwd and rev primers for sequencing to have double confirmation.