The -35 sequence is a conserved DNA pattern in prokaryotic promoters, usually about 35 bases before the transcription start site. It helps sigma factor bind RNA polymerase so transcription can begin in bacteria.
The -35 sequence is a short DNA motif in a prokaryotic promoter, usually found about 35 base pairs upstream of the transcription start site. In General Biology I, you meet it as part of how bacteria turn genes on by recruiting RNA polymerase to the right spot on the DNA.
This region is called the -35 sequence because it sits roughly 35 nucleotides before the +1 site, where transcription actually begins. A common version of the sequence is TTGACA, but the exact bases can vary a little as long as the promoter still works well enough for RNA polymerase to recognize it.
The -35 sequence does not act alone. It works with the -10 sequence, also called the Pribnow box, to create a promoter that sigma factor can recognize. Sigma factor is the part of bacterial RNA polymerase that reads promoter DNA and helps the enzyme bind in the right place. Without that recognition step, the polymerase may bind weakly, bind in the wrong place, or not start transcription efficiently.
Think of the -35 region as one of the landing marks for the transcription machinery. The promoter has to be positioned correctly so the enzyme can line up with the start site. If the spacing between the -35 and -10 elements changes too much, the promoter often works less well because the protein cannot make the right contacts with both regions at once.
Mutations in the -35 sequence can change gene expression by changing how tightly sigma factor binds. A stronger match to the consensus sequence usually makes transcription start more easily, while a weaker match can reduce expression. That is one reason bacteria can have very different levels of gene activity even when the gene itself has not changed much.
The -35 sequence matters because it shows how bacteria control transcription before any RNA is made. Instead of relying on a nucleus or many layers of processing, prokaryotes use promoter DNA sequences to decide whether RNA polymerase can begin.
This term also connects directly to gene regulation. When you see a promoter mutation in a biology problem, the effect is often not a changed protein sequence but a changed level of transcription. A small base change in the -35 region can lower transcription, raise it, or prevent initiation altogether.
General Biology I uses this idea to show that DNA is not just a storage molecule. Its sequence contains instructions for when genes are read, and the promoter is one of the first control points. That is why the -35 sequence matters in topics like operons, bacterial adaptation, and differences in gene expression between cells.
It also gives you a clean way to explain experimental results. If a lab question asks why a bacterial strain makes less mRNA after a promoter mutation, the -35 sequence is one of the first places to look. You are tracing cause and effect from DNA sequence to transcription efficiency to protein output.
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Visual cheatsheet
view galleryPromoter
The -35 sequence is one part of the promoter, not the whole promoter. When you identify a bacterial promoter, you are usually looking for multiple DNA features that help RNA polymerase bind and start transcription. The -35 region works with nearby promoter elements to make initiation efficient and accurate.
Sigma factor
Sigma factor is the protein that recognizes promoter DNA, including the -35 sequence. It guides RNA polymerase to the correct start site and helps the enzyme form a stable initiation complex. If sigma factor cannot match the -35 region well, transcription initiation becomes less efficient.
Pribnow box
The Pribnow box is the -10 sequence, and it works with the -35 sequence during bacterial transcription initiation. The two regions are usually discussed together because both need to be correctly spaced and recognized. A strong promoter often has a good match at both sites.
Transcription initiation
The -35 sequence matters specifically during transcription initiation, before elongation begins. It helps RNA polymerase dock on the promoter and start RNA synthesis at the right nucleotide. If initiation fails, the gene will not be transcribed efficiently no matter how normal the rest of the DNA is.
A quiz question might show a bacterial promoter sequence and ask which part helps RNA polymerase bind first, and you would identify the -35 region by its position upstream and its promoter function. In a mutation problem, you may be asked to predict what happens if the -35 sequence changes, and the safe answer is usually reduced binding of sigma factor and lower transcription.
You can also use it in diagram questions. If a figure labels the +1 site, the -10 box, and the -35 sequence, you should be able to trace the direction of transcription and explain why spacing matters. In short-answer prompts, connect the sequence to initiation rather than to translation or protein structure.
These two promoter elements are often confused because both are part of bacterial transcription initiation. The -35 sequence sits farther upstream, while the Pribnow box is the -10 region closer to the start site. They work together, but they are not the same DNA motif and they do not sit in the same position.
The -35 sequence is a conserved DNA element in prokaryotic promoters, found about 35 bases upstream of the transcription start site.
It helps sigma factor recognize the promoter so RNA polymerase can begin transcription in the correct place.
The -35 sequence works together with the -10 sequence, or Pribnow box, to make bacterial transcription initiation efficient.
Mutations in the -35 region can weaken promoter binding and lower gene expression.
In General Biology I, this term usually shows up when you are tracing how bacteria control which genes get transcribed.
It is a short DNA sequence in a bacterial promoter, usually about 35 base pairs before the transcription start site. Sigma factor recognizes it as part of the setup for transcription initiation. Without a workable -35 region, RNA polymerase has a harder time starting transcription efficiently.
It is located upstream of the +1 transcription start site, roughly 35 bases before transcription begins. That placement matters because promoter elements have to be in the right position for sigma factor and RNA polymerase to bind correctly. If the spacing shifts too much, promoter function can drop.
The -35 sequence and the Pribnow box are both parts of a bacterial promoter, but they sit in different positions. The -35 region is farther upstream, while the Pribnow box is the -10 element closer to the start site. They work together during initiation, so a problem in either one can affect transcription.
A mutation can make it harder for sigma factor to recognize the promoter, which usually lowers transcription. The exact effect depends on how much the sequence changes and whether the promoter still keeps the right spacing with the -10 region. In lab questions, this often shows up as reduced gene expression.