**2. Transcription factors (TFs) in mammalian cells**

Transcription factors are divided into two groups. First, the general TFs (GTFs), including preinitiation complex components TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and THIIH, are the primary protein factors that are required for the initiation of transcription from the TATA box (or TATA element), then elongation is executed by RNA polymerase II (RNA pol II) [1]. The others are the site-specific TFs or the DNA sequence-specific binding proteins.

#### **2.1 The GTFs and TATA-less promoters**

Molecular mechanisms of the initiation of transcription from TATA box have been well known as the most essential nuclear events in mammalian cells. However, about 70% of mammalian gene promoters have no TATA or TATA-like elements, and they are referred to as TATA-less promoters [2]. In yeast cells, most of genes are regulated by the same general TF-dependent system independent of TATA or TATA-like sequences [3]. TATA-containing and TATA-less promoters

are different in the distribution of the A-tracts, G-quadruplex, and CpG islands [4]. Given that most of the housekeeping genes are controlled by TATA or TATAlike elements, TATA-less promoters would be sensitive to the environments in response to various stresses. For example, some of the TATA-less promoters have DTIE binding sites [5]. The duplicated GGAA (TTCC) elements are frequently found near the transcription start sites (TSSs) of the human TATA-less promoters [6], implying that GGAA (TTCC) binding TFs contribute to the initiation of transcription.
